Add ability to pick a different gamut in GPU f16 or sRGB configs

For now, the only options are sRGB or WideGamutRGB

Basically, the color option to the gpu config is now of
the form: 8888|srgb[_gamut]|f16[_gamut]

color=8888 still implies legacy behavior
srgb implies 8-bit gamma-correct rendering (via sRGB format)
f16 implies 16-bit gamma-correct rendering (via F16 format)

Either of the last two options can then optionally include
a gamut specifier, either _srgb or _wide.
_srgb selects the (default) sRGB gamut
_wide selects the Adobe Wide Gamut RGB gamut, which is nice
for testing, in that it's significantly wider than sRGB,
so rendering differences are obvious.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2350003003

Review-Url: https://codereview.chromium.org/2350003003
2 files changed