Auto merge of #26923 - mrobinson:pseudo-animations-2, r=emilio

Add animation and transition support for pseudo-elements

This change extends the DocumentAnimationSet to hold animations for
pseudo-elements. Since pseudo-elements in Servo are not in the DOM like
in Gecko, they need to be handled a bit carefully in stylo.  When a
pseudo-element has an animation, recascade the style. Finally, this
change passes the pseudo-element string properly to animation events.

---
<!-- 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 #10316
- [x] There are tests for these changes

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tests/wpt/metadata-layout-2020/css/css-animations/animationevent-pseudoelement.html.ini

@@ -1,5 +0,0 @@
-[animationevent-pseudoelement.html]
-  expected: TIMEOUT
-  [AnimationEvent should have the correct pseudoElement memeber]
-    expected: TIMEOUT
-

tests/wpt/metadata-layout-2020/css/css-transitions/events-006.html.ini

@@ -1,8 +0,0 @@
-[events-006.html]
-  expected: TIMEOUT
-  [transition padding-left on ::after]
-    expected: NOTRUN
-
-  [transition padding-left on ::before]
-    expected: TIMEOUT
-

tests/wpt/metadata-layout-2020/css/css-transitions/non-rendered-element-002.html.ini

@@ -1,5 +0,0 @@
-[non-rendered-element-002.html]
-  expected: TIMEOUT
-  [Transitions on ::before/::after pseudo-elements are canceled when the content property is cleared]
-    expected: TIMEOUT
-

tests/wpt/metadata-layout-2020/css/css-transitions/pseudo-elements-001.html.ini

@@ -1,13 +0,0 @@
-[pseudo-elements-001.html]
-  [transition padding-left on :before / values]
-    expected: FAIL
-
-  [transition padding-left on :after, changing content / values]
-    expected: FAIL
-
-  [transition padding-left on :before, changing content / values]
-    expected: FAIL
-
-  [transition padding-left on :after / values]
-    expected: FAIL
-

tests/wpt/metadata/css/css-animations/animationevent-pseudoelement.html.ini

@@ -1,6 +0,0 @@
-[animationevent-pseudoelement.html]
-  bug: https://github.com/servo/servo/issues/10316
-  expected: TIMEOUT
-  [AnimationEvent should have the correct pseudoElement memeber]
-    expected: TIMEOUT
-

tests/wpt/metadata/css/css-transitions/events-006.html.ini

@@ -1,9 +0,0 @@
-[events-006.html]
-  bug: https://github.com/servo/servo/issues/10316
-  expected: TIMEOUT
-  [transition padding-left on ::after]
-    expected: NOTRUN
-
-  [transition padding-left on ::before]
-    expected: TIMEOUT
-

tests/wpt/metadata/css/css-transitions/non-rendered-element-002.html.ini

@@ -1,8 +1,4 @@
 [non-rendered-element-002.html]
-  expected: TIMEOUT
-  [Transitions on ::before/::after pseudo-elements are canceled when the content property is cleared]
-    expected: TIMEOUT
-
   [Transitions on ::marker pseudo-elements are canceled when the parent display type is no longer list-item]
     expected: NOTRUN
 

tests/wpt/metadata/css/css-transitions/pseudo-elements-001.html.ini

@@ -2,12 +2,6 @@
   [transition padding-left on :before / values]
     expected: FAIL
 
-  [transition padding-left on :after, changing content / values]
-    expected: FAIL
-
-  [transition padding-left on :before, changing content / values]
-    expected: FAIL
-
   [transition padding-left on :after / values]
     expected: FAIL