Resolve Android resource references (@drawable/name) in memory footprint

[mihais]

Watch faces may reference drawables using the Android resource reference syntax, e.g. resource="@drawable/name", instead of the bare resource name. The Watch Face Format runtime resolves both forms to the same drawable, but the memory footprint validator looked up the raw attribute value in a resource map keyed by bare name and failed with:

Asset @drawable/name was not found in the watch face package

even though the drawable is present in the APK.

Change

• Add WatchFaceDocuments.getResourceReference / normalizeResourceReference, which strip the @type/ (or @package:type/) prefix from a reference. Expressions ([...]), bare names and empty values are returned unchanged.
• Use it for the resource and thumbnail attributes in WatchFaceResourceCollector, and for resource in OptimizationEstimator, so both the footprint evaluation and the optimization estimate find the referenced drawable.

Testing

• New WatchFaceDocumentsTest for the normalization.
• New WatchFaceResourceCollectorTest#collectResources_normalizesAndroidResourceReferences.
• New ResourceMemoryEvaluatorTest layout case (AndroidResourceReferences.xml, a copy of ImageHiddenInActive.xml using @drawable/ references) that expects the same footprint as the bare-name layout.
• ./gradlew spotlessCheck memory-footprint:jar memory-footprint:test passes (135 tests, including GoldenTest). Without the fix, the new reference tests fail with the error above.
• Verified on three real watch faces that use <Image resource="@drawable/...">: they fail on main and pass with this change, with the same reported footprint as when the references are rewritten to bare names.