SDK / exoplayer

Previously, we always used ImageReader to read from the output of DefaultVideoFrameProcessor, for pixel tests. This has a limitation of not being
able to read HDR contents, so that we couldn't support HDR pixel tests.

Reading from a texture allows us to use glReadPixels to read from
DefaultVideoFrameProcessor, and build upon this to implement HDR pixel tests. We do
still want tests for surface output though, because real use-cases only will output
to Surfaces.

Also, add some tests for outputting to textures, since this test infrastructure is
a bit complex.

PiperOrigin-RevId: 519786535