[AGP 9.1.0 Migration #2] Extract internal utilities - #190957

…dependencies through the new DSL (flutter#191218)

This is PR 3 of 11 in the AGP 9.1.0 / public `gradle-api`/ newdsl
migration stack.

* It migrates many (but not all) usages of getLegacyAndroidExtension. 
* Introduces consistency in renaming of imports. 
* Adds a test to ensure we are not adding internal apis (thanks
@mboetger from pr1)
* builds the ability to run our gradle tests with multiple AGP versions
(see packages/flutter_tools/gradle/build.gradle.kts)

Between PR 3 and PR 8, an Add-to-app host app embedding a Flutter module
with a custom build type (for example "staging") gets release engine
artifacts. That means hot reload, debugger attach, and DevTools do not
operate in that build.
We can't move the work in PR 8 up but I would not want to cut a release
between this pr and 8 landing. If we keep reviewing one pr a day then
that is not a risk.

Apps impacted by this change can use matchingFallbacks to avoid this
problem (see code below).

In pr 8 we change when we look for "isDebuggable" to much later in the
gradle lifeycle when all the variants have been created which then lets
us use a new api to understand if the variant is intended to be
debuggable.

Kotlin 
```kotlin
// host app build.gradle.kts
android {
    buildTypes {
        create("staging") {
            isDebuggable = true
            applicationIdSuffix = ".staging"
            matchingFallbacks += "debug" /// This line. 
        }
    }
}
```
Groovy 
```groovy
// host app build.gradle
android {
    buildTypes {
        staging {
            debuggable true
            applicationIdSuffix ".staging"
            matchingFallbacks = ['debug'] /// This line. 
        }
    }
}
```

Depends on flutter#190957 (PR 2).
- @reidbaker 


---
Standard review context for this pr stack

This is PR is part of an 11 pr stack to migrate the "newdsl"
`gradle-api` specifically in agp 9.1.0.
The complete stack has passed presubmits, postsubmits, and customer
tests:
https://flutter-dashboard.appspot.com/#/build?repo=flutter&branch=experimental/agp-gradle-api

All of the code was LLM authored. A mix of manual prompting, automatic
prompting, several models and adversarial review. The combined sessions
are enough that I cannot include relevant prompts like I have been doing
on other prs.

If you want to review the pr stack you can find it here. These prs will
be abandoned/closed as prs land into flutter/flutter.
1. reidbaker-agent#1 (branch:
agp-api-doc)
2. reidbaker-agent#2 (branch:
agp-internal-utils)
3. reidbaker-agent#3 (branch:
agp-buildmode-deps)
4. reidbaker-agent#4 (branch:
agp-plugin-buildtypes)
5. reidbaker-agent#5 (branch:
agp-ndk-fallback)
6. reidbaker-agent#6 (branch:
agp-assets-onvariants)
7. reidbaker-agent#7 (branch:
agp-apk-copy-versioncode)
8. reidbaker-agent#8 (branch:
agp-add-to-app)
9. reidbaker-agent#9 (branch:
agp-aar-script)
10. reidbaker-agent#10 (branch:
agp-newdsl-flip)
11. reidbaker-agent#11 (branch:
agp-gradle-api)

This work is urgent in the sense that we are worried that android will
publish agp 10 with no opt out but not so urgent that we are willing to
break flutter users because we didn't review or understand the code
because we were in a rush.

Breaking changes are expected as part of this work. There are patterns
the android team explicitly does not want apps to use and apis that have
no equivalent.

As part of the effort to ensure this work does not slip into ai slop,
prs from this stack will be reviewed by me (@reidbaker) before asking
for review. Then we will have 2 android expert reviewers also review
every pr.

--- 
Agent authored description. 
This is PR 3 of 11 in the AGP 9.1.0 / public `gradle-api` migration
stack (flutter#180137, flutter#166550).

### Key Changes
- **DSL Build Mode Overloads**: Adds `buildModeFor` overloads accepting
`ApplicationBuildType`, `DynamicFeatureBuildType`, and
`LibraryBuildType` DSL types alongside the `(buildTypeName,
isDebuggable)` core overload.
- **Robust CompileSdkVersion Domain Model**: Extracts
`CompileSdkVersion` with constructor invariant validation (`init {
require(...) }`) enforcing mutual exclusivity between `apiLevel` and
`previewCodename`.
- **Namespaced Multi-AGP Build Property**: Namespaces the AGP version
property in `packages/flutter_tools/gradle/build.gradle.kts` as
`flutter.internal.agpVersion` (defaulting to `8.11.1`) to prevent user
app properties from leaking into the included build during app
compilation.
- **Standardized Type Aliasing**: Applies non-temporal type aliasing
(`import com.android.build.api.dsl.BuildType as DslBuildType`) across
`FlutterPlugin.kt` and `PluginHandler.kt`.
- **Public DSL Extension Access**: Updates `addFlutterDependencies` and
`PluginHandler` to iterate `AgpCommonExtensionWrapper.buildTypes`.
- **Build & Bytecode Validation**: Adds the
`:validateNoCommonExtensionInBytecode` task in `build.gradle.kts` to
prevent compiled main classes from referencing binary-incompatible
`CommonExtension`, and adds `BytecodeValidatorTest.kt` verifying the
binary pattern-matching and class scanning logic.
- **Comprehensive Unit Tests**: Adds full 4-way dispatch test coverage
in `AgpCommonExtensionWrapperTest`, dependency wiring tests in
`FlutterPluginTest`, and decomposes `PluginHandlerTest` mock fixtures
into focused helpers with positive assertions.

### Add-to-App & DSL Scope Context
`LibraryBuildType` does not expose `isDebuggable` at DSL scope. In PR 3,
custom build types on library projects (e.g. host app 'staging') fall
back to `"release"` at DSL scope. In PR 8 ("Unify add-to-app module
wiring on the variant API"), module wiring will be unified on
`Component.debuggable` at variant scope.

## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [AI contribution guidelines] and understand my
responsibilities, or I am not using AI tools.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [x] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [x] All existing and new tests are passing.

---------

Co-authored-by: reidbaker-agent <reidbaker@google.com>
Co-authored-by: Reid Baker <1063596+reidbaker@users.noreply.github.com>

…91281)

## Description

This closes out flutter#191081. The bogus "compiles against Android SDK
2147483647" warning was caused by `getCompileSdkFromProject` parsing the
deprecated `compileSdkVersion` platform-hash string
(`"android-36-ext19".substring(8).toIntOrNull() ?: Int.MAX_VALUE`).

That codepath no longer exists: flutter#190957 (part of the AGP 9.1.0 migration
stack) already rewrote `getCompileSdkFromProject` to read AGP's typed
`compileSdk: Int?` / `compileSdkPreview: String?` DSL properties
directly. Since `compileSdk` never folds in the extension suffix, the
failure mode in flutter#191081 is now structurally impossible — no plugin's
`compileSdkExtension` can leak into this comparison.

What was missing was test coverage for exactly this scenario (a plugin
with `compileSdkExtension` set, as required by AARs with a
`minCompileSdkExtension` metadata constraint — e.g.
`androidx.health.connect:connect-client`). This PR adds that regression
test to `FlutterPluginUtilsTest.kt`, confirming `compileSdkExtension`
plays no part in the resulting `CompileSdkVersion` or in `isHigherThan`
comparisons, so a future refactor can't reintroduce the bug.

No production code changes — this is test-only.

## Pre-launch Checklist

- [x] I read the [Contributor
Guide](https://github.com/flutter/flutter/blob/master/docs/contributing/Tree-hygiene.md)
and followed the process outlined there for submitting PRs.
- [x] I read the [Tree
Hygiene](https://github.com/flutter/flutter/blob/master/docs/contributing/Tree-hygiene.md)
wiki page, which explains my responsibilities.
- [x] I read and followed the [Flutter Style
Guide](https://github.com/flutter/flutter/blob/master/docs/contributing/Style-guide-for-Flutter-repo.md).
- [x] I signed the [CLA](https://cla.developers.google.com/).
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I added new tests to check the change I am making.

Fixes flutter#191081

Co-authored-by: Devasy Patel <110348311+Devasy23@users.noreply.github.com>
Co-authored-by: Reid Baker <1063596+reidbaker@users.noreply.github.com>
Co-authored-by: Camille Simon <43054281+camsim99@users.noreply.github.com>