Add runtime decoder switching

[anilbeesetti]

Summary

• add DecoderManager for independent runtime video and audio decoder selection
• support hardware MediaCodec, system software MediaCodec, bundled FFmpeg, and nullable automatic selection without recreating ExoPlayer
• integrate the manager with NextRenderersFactory and expose the active decoder modes from analytics callbacks
• document the API and add focused manager/renderer-controller tests
• align the library with Media3 1.11.0 and release version 0.14.0

Testing

• ./gradlew :media3ext:testDebugUnitTest :media3ext:assembleRelease
• git diff --check