Auto merge of #12118 - emilio:animation-shorthand, r=SimonSapin

style: Add support to the animation shorthand and fix parsing of animation-name

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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors

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Part of #11916.

r? @SimonSapin

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tests/wpt/metadata-css/css-flexbox-1_dev/html/css-flexbox-height-animation-stretch.htm.ini

@@ -0,0 +1,4 @@
+[css-flexbox-height-animation-stretch.htm]
+  type: reftest
+  expected: TIMEOUT
+  bug: https://github.com/servo/servo/issues/12328

tests/wpt/metadata-css/css-transitions-1_dev/html/transition-timing-function-001.htm.ini

@@ -1,8 +1,5 @@
 [transition-timing-function-001.htm]
   type: testharness
-  [parse 'steps(3)']
-    expected: FAIL
-
   [parse 'cubic-bezier(-0.1, -0.2, -0.3, -0.4)']
     expected: FAIL