feat(hilt): Add limited dynamic feature module support for tests

[Senthil455]

When applying the Hilt plugin to a dynamic feature module (com.android.dynamic-feature), AGP provides a DynamicFeatureAndroidComponentsExtension which was not handled by the plugin's type checks, causing the error:

Failed to apply plugin 'com.google.dagger.hilt.android'.
Hilt plugin does not know how to configure 'extension 'androidComponents''

Changes

This change adds support for dynamic feature modules in a limited capacity by handling DynamicFeatureAndroidComponentsExtension in two key locations:

1. Variants.kt (\onRootVariants) - Dynamic feature modules are treated like libraries: only test variants (unitTest and androidTest) are configured as Hilt roots where component trees are generated.

2. HiltGradlePlugin.kt (\configureProcessorFlags) - Dynamic feature modules are assigned \GradleProjectType.LIBRARY\ since they cannot have a @HiltAndroidApp.

3. GradleProjectType.java - Updated the Javadoc to reflect that dynamic features are now supported in a limited capacity.

Design Rationale

• Dynamic feature modules cannot contribute bindings/modules to the main app's monolithic graph
• They should be able to create test-specific graphs for writing unit tests and instrumentation tests
• The library behavior is the right model: only test variants generate Hilt components
• @HiltAndroidApp is still correctly rejected in dynamic features (enforced by AndroidEntryPointProcessingStep's GradleProjectType.APP check)
• The bytecode transform (onAllVariants) still applies to all variants since @androidentrypoint classes may exist in tests

Fixes #5089

[bcorso]

I think we will want to enforce this, e.g. by having a lint check to ensures no @InstallIn usages in the main source set of a DFM, i.e. they are only allowed within the test source sets. See https://github.com/google/dagger/tree/master/dagger-lint.

This prevents cases where your DFM accidentally adds a new @InstallIn module or entry point in non-test sources and the test passes (because the test generates a new component that includes this metadata), but fails in production.

[bcorso]

Can you also add a Gradle test to https://github.com/google/dagger/tree/master/javatests/artifacts/hilt-android to ensure we have test coverage for this.