Extract an interface SurfaceCapture from ScreenEncoder, representing a
video source which can be rendered to a Surface for encoding.
Split ScreenEncoder into:
- ScreenCapture, implementing SurfaceCapture to capture the device
screen,
- SurfaceEncoder, to encode any SurfaceCapture.
This separation prepares the introduction of another SurfaceCapture
implementation to capture the camera instead of the device screen.
Co-authored-by: Romain Vimont <rom@rom1v.com>
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