Revert: Fix square corner issue - #193189

Reverts: Fix square corner issue

Initiated by: @andywolff

Reason for reverting: seems to have caused a test order dependency #192992
Original PR Author: @andywolff

Reviewed By: @gaaclarke

The original PR description is provided below:

Fixes #190602, see my comment on that issue for details about the problems I identified.
Also fixes #162172

What changed

When a route contained rounded clips (such as CupertinoSheetRoute), intermediate child ink features, and a backdrop filter (such as a blurred app bar), the clip stack replay logic prematurely popped parent clips and exceeded the depth buffer budget across render pass splits, causing subsequent header draws to render with 90° square corners. This PR addresses both mechanisms:

First, EntityPassClipStack::RecordRestore was popping replay entities unconditionally whenever any clip was restored. In a sheet containing ink decorations (like list item ripple effects), child clip restores at deeper heights would prematurely discard the root parent clip. We now track clip_height in ReplayResult so that restorations only pop entities when clip_height > restore_height, preserving parent clips across sibling restores. When replaying those clips in ClipContents::Render, we also supply the entity's model matrix to properly recompute the MVP matrix against the new pass's orthographic projection instead of reusing the stale matrix from the prior pass.

Second, the pass depth budget was exhausting across backdrop splits. Canvas::kMaxDepth (1 << 24) was mismatched with Entity::kDepthEpsilon (1.0 / 262144.0, or 2^-18), allowing integer depths to exceed the 18-bit precision of the depth buffer. Aligning Canvas::kMaxDepth to 262,143 and capping depth allocations in Save/SaveLayer to min(current_depth_ + total_content_depth, parent_clip_depth) keeps clip replay and subsequent draw operations within valid precision bounds. In Canvas::Restore, we also prevent unconditional depth jumps to kMaxDepth for unclipped saves, preserving the allocated budget for subsequent sibling draws.

Testing

Reproducing this interaction in automated tests required testing the onscreen pass-splitting branch (IsOnscreen()), which normal offscreen unit tests bypass. We added a ScopedOnscreenOverride test hook in Canvas and constructed a multi-layer display list recreating the route clip, child ink items, blurred backdrop bar, and trailing app bar:

• clip_stack_unittests.cc: Added EntityPassClipStackTest.RestoringChildClipPreservesParentReplayEntities to isolate parent clip retention across sibling restores.
• canvas_unittests.cc: Added AiksTest.ClipDepthMaintainedAcrossBackdropFilterAndLayers to verify depth invariants and precision bounds (<= kMaxDepth), and AiksTest.ParentClipDepthBudgetPreservedAfterBackdropLayerRestore to verify parent depth budget restoration.
• dl_golden_unittests.cc (impeller_golden_tests): Added DlGoldenTest.CanRenderClippedBackdropFilterWithSuperellipse for pixel-accurate golden image verification in CI against Skia Gold.

Pre-launch Checklist

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