Rename lots of things from 'sRGB' to 'GammaCorrect', where appropriate

Trying to be much more explicit about where we really mean sRGB as a format,
and where we mean gamma-correct, as in: "not legacy behavior". Most of the
changes to rendering behavior are dependent on the latter, so let's be precise.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1884873006

Review URL: https://codereview.chromium.org/1884873006
27 files changed