[css-ui-3][css-ui-4][editorial] Added WPTs

[SebastianZ]

I added all the Web Platform Tests that currently cover the features in CSS UI 3 and 4.

Note that this PR does not include hints about missing WPT coverage or notes about tests not being necessary for specific sections. Those should be added separately.

Sebastian

[frivoal]

Without reviewing every single test in detail, which seems like more work than I can justify at the moment, a review of this PR can only somewhat shallow, but having looked through it at that high level, it seems fine.

I think <wpt> annotation should ideally be spread through the spec and be inserted after each paragraph that describes something testable, rather than grouped at the start of each section, but doing so takes a tremendous amount of work, and getting the tests into the right sections, as this PR does, is already useful.

I left a few minor comments, but overall, this seems fine.

[SebastianZ]

think <wpt> annotation should ideally be spread through the spec and be inserted after each paragraph that describes something testable, rather than grouped at the start of each section, but doing so takes a tremendous amount of work, and getting the tests into the right sections, as this PR does, is already useful.

I agree they should ideally be moved to the paragraphs they belong to. Though it already took quite some time to add all the 1312 tests.😅 So that may be done in a follow-up change.

Sebastian

[SebastianZ]

@frivoal Thank you for the approval! Please note that I added a last change that restructured the Changes section to be consistent with the one of level 4 and added a note about the WPTs there.

Sebastian