Add disabled user counters for RGB, OkLabOkLch, and out-of-Rec2020

Add counters for the CSS Color Level 4 syntax, dividing the syntax
into the classes of RGB spaces versus OkLab/OkLch (OkLxx). For these
two classes, track how often they specify a color outside of the
Rec2020 gamut.

This is to inform choices about how to handle out-of-range values
in the OkLab/OkLch syntax.

Mark the counters kCSSColorColorSpecifiedSpace, kCSSColorLabOklab,
and kCSSColorLchOklch obsolete, because they were observed not to be
used anymore.

Previously landed in crrev.com/1256189
Reverted in crrev.com/1256383
Reason for revert fixed in crrev.com/1256784
Landed again in crrev.com/1269624
Reverted again in crrev.com/1269624

Reverts are because evaluating pow() with a negative value causes
asserts (see b/40949047). Leave disabled by default.

Bug: 40949047
Change-Id: Id879c5357ca64e795c69ed407795a05d89a39e56
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5398498


Commit-Queue: ccameron chromium <ccameron@chromium.org>
Reviewed-by: Philip Jägenstedt <foolip@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1278695}