Use the correct dataspace in shaders.cpp

This improves the quality of HDR->SDR tone-mapping in TextureView by
removing an incorrect gamut mapping which was causing undesired hue
shift.

The technical detail is that in TextureView, skia will color manage the
input image to the destination colorspace prior to tone-mapping. The
tone-mapping shader library compensates when authoring the shader to use
the correct EOTF when re-decoding the image, but did not compensate when
binding uniforms. This patch compensates accordingly so that the correct
gamut->gamut mapping is applied.

This patch adds a brief test suite for libshaders to verify that the
correct color gamut matrices are being selected.

Bug: 234355355
Test: Observe accurate HLG colors in Photos and Instagram where
TextureView is used for media playback.
Test: libshaders_test

Change-Id: I801349cfe1780880a55528fd7e91ff1ac553281b