Move some of the CSSStyleDeclaration logic to the style crate
<!-- Please describe your changes on the following line: -->
… so that Stylo can re-use it.
Fixes https://bugzilla.mozilla.org/show_bug.cgi?id=1295865
---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [ ] These changes fix #__ (github issue number if applicable).
<!-- Either: -->
- [ ] There are tests for these changes OR
- [x] These changes do not require tests because refator
<!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. -->
<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/13640)
<!-- Reviewable:end -->
Fix Issue 12343: Add pref-gated methods and test for activatable element
<!-- Please describe your changes on the following line: -->
Add methods to activatable elements; gated by a preference, for use in servo-specific WPT tests.
I cargo-culted over the "redundant check" from #12322, I don't really understand the possible exploit.
Obvious flaw is the copypasta for each element. I understand that the webidl codegen will produce a trait for ActivatableElement, but I can't see how I can provide a default implementation for this? I guess otherwise could be an improvement to have each element just delegate to an Enter.../Exit... method on the Activatable trait?
---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix#12343 (github issue number if applicable).
<!-- Either: -->
- [X] There are tests for these changes OR
- [ ] These changes do not require tests because _____
<!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. -->
…states
<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/12703)
<!-- Reviewable:end -->
Issue 8719: Add basic support for :active selector
<!-- Please describe your changes on the following line: -->
Added toggling of active state for element and parents on mousedown/mouseup. Active state is removed when mouseout. (hover)
- As with my other PR i'm struggling a bit with the automated testing. I've added a manual test case and found quirks-mode/active-and-hover-manual.html which - aside from also being a manual test, is functional in Firefox but does not render correctly in Servo.
- Not implemented: In Firefox, behaviour differs with a <!DOCTYPE HTML> and an anchor does not lose it's activation on mouseout; whereas a button does.
---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix#8719 (github issue number if applicable).
<!-- Either: -->
- [ ] There are tests for these changes OR
- [ ] These changes do not require tests because _____
<!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. -->
<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="35" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/11781)
<!-- Reviewable:end -->
