This allows us to use BT.2020 RGB linear for intermediate shaders, which also
allows us to re-enable PeriodicVignetteProcessor, which should work properly in
linear color-spaces.
Manually tested by adding a GlEffectsWrapper, and confirming that HLG HDR editing still looks correct.
PiperOrigin-RevId: 462265821
(cherry picked from commit 1ecf1eb7)
