Auto merge of #26200 - mrobinson:animation-iterator, r=emilio

style: Add an iterator for transition properties

This simplifies the code a bit and also will allow us to more easily
make improvements to servo's animation implementation in the future.

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---
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- [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)

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- [ ] There are tests for these changes OR
- [x] These changes do not require tests because they should not change behavior.

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tests/wpt/metadata/css/css-transitions/events-005.html.ini

@@ -2,9 +2,6 @@
   [padding-left, padding]
     expected: FAIL
 
-  [padding, padding-left]
-    expected: FAIL
-
   [property repetition]
     expected: FAIL
 

tests/wpt/metadata/css/css-transitions/properties-value-002.html.ini

@@ -2,27 +2,3 @@
   [vertical-align vertical(keyword) / values]
     expected: FAIL
 
-  [margin-right percentage(%) / events]
-    expected: FAIL
-
-  [padding-top percentage(%) / events]
-    expected: FAIL
-
-  [margin-top percentage(%) / events]
-    expected: FAIL
-
-  [margin-bottom percentage(%) / events]
-    expected: FAIL
-
-  [padding-right percentage(%) / events]
-    expected: FAIL
-
-  [padding-left percentage(%) / events]
-    expected: FAIL
-
-  [padding-bottom percentage(%) / events]
-    expected: FAIL
-
-  [margin-left percentage(%) / events]
-    expected: FAIL
-