Introduce PolygonShape and PolygonShapeGeometry

- Adds PolygonShape in Compose Foundation backed by graphics-shapes RoundedPolygon, enabling resolution-aware polygons, stars, pills, and author-space unit geometries with per-vertex and uniform corner rounding.

- Adds PolygonShape, PolygonShapeGeometry, PolygonShapeGeometry.CornerRounding, and PolygonShapeScope.
- Provides named companion factories for common regular polygons, stars, pill stars, and rectangles.

Test: ./gradlew :compose:foundation:foundation:connectedAndroidTest -Pandroid.testInstrumentationRunnerArguments.
  class=androidx.compose.foundation.shape.PolygonShapeTest
Relnote: "Introduces `PolygonShape` in Compose Foundation for rendering regular, star, and custom rounded polygons with corner smoothing."
Fixes: 378826438
Change-Id: I0b99d9ad53f21a71f283e830e63806add4b3b51b