SDK / exoplayer

- Add a checkbox in the demo app to enable experimental HDR editing.
- Add an `experimental_` method to `TransformationRequest` to enable HDR editing.
- Add fragment/vertex shaders for the experimental HDR pipeline. The main difference compared to the existing shaders is that we sample from the decoder in YUV rather than RGB (because the YUV -> RGB conversion in the graphics driver is not precisely defined, so we need to do this to get consistent results), which requires the use of ES 3, and then do a crude YUV -> RGB conversion in the shader (ignoring the input color primaries for now).
- When HDR editing is enabled, we force using `FrameEditor` (no passthrough) to avoid the need to select another edit operation, and use the new shaders. The `EGLContext` and `EGLSurface` also need to be set up differently for this path.

PiperOrigin-RevId: 425570639