[css-color-4] Testable but untested sections

[svgeesus]

(edited to reflect content moved to Color 5)

• Color Space of Tagged Images

Added must-match and must-not-match tests with tagged and untagged images (at least for JPEG and PNG)

• Color Spaces of Untagged Colors

• Add untagged images and corresponding css-styled patches

• Add bgcolor? and corresponding css-styled patches

• Serializing Values

color-computed.html has 236 tests

• The transparent keyword
  Has 24 tests

• Converting predefined color spaces to Lab or OKLab

• Converting Lab or OKLab to predefined RGB color spaces

These looked to be untested but some tests were in fact testing these conversions so I tagged them

• Transparency: the opacity property

• 6 tests

• Interpolation

Tested by the color-mix()` tests, and tagged to Interpolation as well.

• Appendix A: Deprecated CSS System Colors

All the "same as" statements are tested results.

[svgeesus]

Also none values. See #6107

[svgeesus]

Also 9.4. Specifying OKLab and OKLCH: the oklab() and oklch() functional notations

[svgeesus]

I have a PR for 5 tagged and untagged image tests looking for a reviewer

[svgeesus]

Opacity has some tests, mainly CSS 2.1 or CSS3 Color tests that need to be (checked and) retagged for CSS Color 4

$ grep -l opacity *.*
body-opacity-0-to-1-stacking-context.html
composited-filters-under-opacity-ref.html
composited-filters-under-opacity.html
inheritance.html
inline-opacity-float-child.html
opacity-overlapping-letters-ref.html
opacity-overlapping-letters.html
t32-opacity-basic-0.0-a.xht
t32-opacity-basic-0.6-a.xht
t32-opacity-basic-1.0-a.xht
t32-opacity-clamping-0.0-b.xht
t32-opacity-clamping-1.0-b.xht
t32-opacity-offscreen-b.xht
t32-opacity-offscreen-multiple-boxes-1-c.xht
t32-opacity-offscreen-multiple-boxes-2-c.xht
t32-opacity-offscreen-with-alpha-c.xht
t32-opacity-zorder-c-ref.html
t32-opacity-zorder-c.xht
t422-rgba-a0.0-a.xht
t422-rgba-a0.6-a.xht
t422-rgba-onscreen-b.xht
t422-rgba-onscreen-multiple-boxes-c.xht
t425-hsla-onscreen-b.xht
t425-hsla-onscreen-multiple-boxes-c.xht

[svgeesus]

All sections now have tests