fix(elements): support exposed host directive bindings - #70334

PR Checklist

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• The commit message follows our guidelines: https://github.com/angular/angular/blob/main/contributing-docs/commit-message-guidelines.md
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

No documentation changes are required because this fixes existing custom-element behavior without introducing a new public API.

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• angular.dev application / infrastructure changes
• Other... Please describe:

What is the current behavior?

When a component that exposes host directive inputs or outputs is converted to a custom element with createCustomElement, those exposed bindings are not included in the custom-element API.

As a result, exposed host directive inputs cannot be set through element properties or attributes, and exposed host directive outputs are not dispatched as custom-element events.

Issue Number: #53193

What is the new behavior?

Custom elements now include host directive bindings that are explicitly exposed by the component.

The implementation:

• reuses Angular's runtime host directive resolution instead of duplicating host directive traversal and alias handling;
• exposes host directive input aliases as custom-element properties and observed attributes;
• keeps input writes routed through ComponentRef.setInput, preserving Angular's input transforms, signal-input behavior, and change detection;
• resolves host directive instances from the component injector for input reads and output subscriptions;
• dispatches exposed host directive outputs using their public aliases;
• does not expose host directive inputs or outputs that are not part of the component's public host-directive API.

Regression tests cover exposed input aliases, input transforms, values set before and after connection, signal input getters, output events, and hidden host directive inputs.

Does this PR introduce a breaking change?

• Yes
• No

Other information

Fixes #53193.