SDK / exoplayer

* Introduced `useHdr` for `GlEffect#toGlTextureProcessor`, so
  `TextureProcessor` implementations can decide how to handle HDR.
* Creating FP16 color textures for HDR input.

Tested via manual testing, adding a no-op GlEffectWrapper to the transformation to
force use of intermediate textures, adding a linear ramp to the fragment shader,
and trying to ascertain that there's a real reduction in posterization when
switching from 4-bit to 8-bit unsigned bytes, and again from 8-bit unsigned bytes
to 16-bit floating point.

PiperOrigin-RevId: 461613117