Add CSSSignRelatedFunctions flags and implement abs(), sign()

According to the CSS Values and Units Module Level 4 [1], abs() and sign() functions should be parsed and evaluated.

Therefore, add a feature flag 'CSSSignRelatedFunctions' and implementations of abs() and sign() functions with CreateSignRelatedFunctionSimplified.

And allow negative zero in CSS math expressions by early return if zero and sign binary is 1.

I2S: https://groups.google.com/a/chromium.org/g/blink-dev/c/okJfodMmuQY

Bug: 1407476
Change-Id: I0f3879eb5c533037341b79d23048d014273516bc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4227272
Reviewed-by: Mason Freed <masonf@chromium.org>
Commit-Queue: Seokho Song <seokho@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1110752}