feat: android screen share audio

[Brazol]

This PR adds support for screen sharing audio on Android by mixing the microphone audio with recorded screen audio.

[Copilot]

Pull request overview

This PR adds support for capturing and mixing screen audio with microphone audio during Android screen sharing. The implementation uses Android Q's (API 29+) AudioPlaybackCaptureConfiguration to capture system audio and mixes it with the microphone stream in real-time.

Key changes:

• Introduces screen audio capture via ScreenAudioCapturer using MediaProjection
• Implements PCM audio mixing with clipping in AudioBufferMixer
• Integrates audio mixing into the WebRTC audio pipeline through the audio buffer callback

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 16 comments.

Show a summary per file

File	Description
ScreenAudioCapturer.java	New class to capture screen audio using AudioPlaybackCaptureConfiguration (Android Q+)
AudioBufferMixer.java	New utility class to mix two PCM 16-bit audio buffers with clipping
OrientationAwareScreenCapturer.java	Adds MediaProjection listener interface and improves lifecycle management with isStopping flag and defensive error handling
MethodCallHandlerImpl.java	Integrates screen audio mixing by adding audio buffer callback and microphone mute detection
GetUserMediaImpl.java	Manages screen audio capture lifecycle, parses includeAudio constraints, and coordinates with MediaProjection events

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