Various fixes for wide color gamut rendering

This CL addresses multiple issues:
- A logic issue where the wide gamut color mode was not set at the right time
- The presence of scRGB surfaces was not detected
- The sRGB to Display P3 matrix was transposed
- The color matrix was applied in gamma space instead of linear space*
- The GPU code path was doing a division by w for each pixel when a
  color transform is set, which shouldn't be necessary (the code now
  checks that the matrix has the expected form)
- Incorrect comment
- Dead code in Description.cpp (mDirtyUniforms was never used)
- Screenshots were taken using the last render engine configuration,
  the configuration is now properly set every time

* This can in theory cause a discrepancy when we switch to/from hardware
  composer mode. I was not able to create a visible discrepancy in practice
  using Night Light, color blindness compensation modes and color inversion.
  More importantly, how/where the hardware composer applies the color
  transform is not specified: it could be gamma or linear space, before or
  after the hardware color LUT. We'll address this in a future CL if needed.
  In addition, this code assumes that fp16 surfaces are encoded in non-linear
  space (scRGB-nl instead of scRGB) but we do not have EGL/Vulkan extensions
  to specify this behavior. We need to address this as well

This CL also fixes potential divides by 0 in the GPU code path.

Bug: 29940137
Test: CtsUiRenderingTestsCases, CtsGraphicsTestCases

Change-Id: I9ae15850f8b9d48c39ebc2724ca3da202be9b008