chore: enable Kotlin explicitApi() and Binary Compatibility Validator (.api dumps)

[dkhawk]

Addresses #1794 in a stacked PR on top of #1716 (feat/migrate-ktx-to-utils).

Summary of Changes

1. Enable Kotlin Explicit API Mode:

   • Configured kotlin { explicitApi() } in library/build.gradle.kts, clustering/build.gradle.kts, data/build.gradle.kts, heatmaps/build.gradle.kts, and ui/build.gradle.kts.
   • Updated all existing Kotlin source declarations with explicit visibility modifiers and explicit return types across all 5 published library modules.

2. Configure Binary Compatibility Validator (BCV):

   • Wired BCV v0.18.2 in build-logic/convention/src/main/kotlin/PublishingConventionPlugin.kt and root build.gradle.kts to support AGP 9.3 compiled release classes (bundleLibCompileToJarRelease / classes.jar).
   • Registered apiBuild, apiDump, and apiCheck tasks per library module with R and BuildConfig exclusion filters.
   • Registered aggregate apiDump and apiCheck verification tasks on root project and wired check to depend on apiCheck.

3. Baseline .api Dumps:

   • Generated and committed baseline public API dumps for:
     • library/api/library.api
     • clustering/api/clustering.api
     • data/api/data.api
     • heatmaps/api/heatmaps.api
     • ui/api/ui.api

4. CI Workflow:

   • Added apiCheck to the PR test workflow in .github/workflows/test.yml.

Fixes #1794

[googlemaps-bot]

Code Coverage

Overall Project	53.65% -1.85%	🍏
Files changed	67.52%	🍏

Module	Coverage
Kover Gradle Plugin XML report for :library	87.74% -0.07%	🍏
Kover Gradle Plugin XML report for :heatmaps	85.02% -0.45%	🍏
Kover Gradle Plugin XML report for :ui	75.3%	🍏
Kover Gradle Plugin XML report for :data	50.48% -3.18%	🍏
Kover Gradle Plugin XML report for :clustering	32.93% -0.69%	🍏

Files

Module	File	Coverage
Kover Gradle Plugin XML report for :library	StreetViewJavaHelper.kt	100%	🍏
	MathUtil.kt	100%	🍏
	SphericalUtil.kt	99.71%	🍏
	PolyUtil.kt	99.37%	🍏
	MapObjectManager.kt	97.1%	🍏
	MarkerManager.kt	81.43%	🍏
	PolygonManager.kt	81.08%	🍏
	CircleManager.kt	81.08%	🍏
	GroundOverlayManager.kt	81.08%	🍏
	PolylineManager.kt	81.08%	🍏
	StreetViewUtil.kt	34.02% -1.66%	🍏
Kover Gradle Plugin XML report for :heatmaps	WeightedLatLng.kt	100%	🍏
	Gradient.kt	88.4% -1.9%	🍏
	HeatmapTileProvider.kt	87.65%	🍏
Kover Gradle Plugin XML report for :ui	AnimationUtil.kt	92%	🍏
	IconGenerator.kt	89.85%	🍏
	RotationLayout.kt	62.5%	🍏
	SquareTextView.kt	0%	🍏
Kover Gradle Plugin XML report for :data	Point.kt	100%	🍏
	Style.kt	100%	🍏
	Feature.kt	100%	🍏
	GroundOverlayStyle.kt	100%	🍏
	Geometry.kt	100%	🍏
	GeoJsonObjects.kt	96.92%	🍏
	LatLngAlt.kt	91.67%	🍏
	KmlParser.kt	90.53% -5.33%	❌
	GeoJsonParser.kt	89.39% -1.4%	❌
	GpxParser.kt	88.68% -8.49%	❌
	KmzParser.kt	87.85% -0.4%	🍏
	KmlMapper.kt	87.36%	🍏
	DataLayer.kt	87.35%	🍏
	Layer.kt	86.05%	🍏
	GpxMapper.kt	69.05% -3.4%	❌
	GroundOverlay.kt	65.31%	🍏
	MapViewRenderer.kt	60.7%	🍏
	GeoJsonPolygon.kt	56.25% -2.5%	🍏
	GeoJsonMapper.kt	56.25%	🍏
	KmlModel.kt	54.26% -0.6%	🍏
	GpxModel.kt	52.22% -1.37%	🍏
	DataScene.kt	52.22% -17.78%	❌
	UrlIconProvider.kt	48.9%	🍏
	Style.kt	39.02%	🍏
	KmlPolygon.kt	32.22% -3.33%	🍏
	GeoJsonPolygonStyle.kt	19.17%	🍏
	GeoJsonLineStringStyle.kt	15.87%	🍏
	GeoJsonPointStyle.kt	15.82%	🍏
	GoogleMapRenderer.kt	0.76% -0.96%	❌
	DataLayerLoader.kt	0%	🍏
	KmlStyle.kt	0%	🍏
	Model.kt	0%	❌
	MapObject.kt	0%	🍏
	Polyline.kt	0% -99.13%	❌
	Layer.kt	0% -18.75%	❌
	Marker.kt	0% -99.16%	❌
	Circle.kt	0% -98.85%	❌
	Polygon.kt	0% -94.87%	❌
Kover Gradle Plugin XML report for :clustering	SphericalMercatorProjection.kt	100%	🍏
	CentroidNonHierarchicalDistanceBasedAlgorithm.kt	100%	🍏
	NonHierarchicalViewBasedAlgorithm.kt	100%	🍏
	AbstractAlgorithm.kt	100%	🍏
	ScreenBasedAlgorithmAdapter.kt	100%	🍏
	GridBasedAlgorithm.kt	100%	🍏
	PreCachingAlgorithmDecorator.kt	100%	🍏
	StaticCluster.kt	100%	🍏
	Bounds.kt	100%	🍏
	ContinuousZoomEuclideanCentroidAlgorithm.kt	99.63%	🍏
	NonHierarchicalDistanceBasedAlgorithm.kt	99.48%	🍏
	Point.kt	94.87%	🍏
	PointQuadTree.kt	94.71%	🍏
	ClusterManager.kt	71.59%	🍏
	DefaultClusterRenderer.kt	14.86% -0.84%	❌
	ClusterRendererMultipleItems.kt	0.15% -0.97%	❌
	DefaultAdvancedMarkersClusterRenderer.kt	0% -1.22%	❌