Auto merge of #12572 - craftytrickster:10933/shorthands, r=emilio

10933/shorthands

<!-- Please describe your changes on the following line: -->
This implements the serialization of nearly all of the css shorthand properties with the following exceptions:

1. font - this may be implemented correctly, but I am not 100% sure
2. border-radius - I do not know how to implement this, since I am not familiar with how the property works
3. background - this is implemented, but I think that the implementation might be a tiny bit off.

---
<!-- 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 #10933  (github issue number if applicable). Also fixes issue #11448

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- [X] There are tests for these changes OR
- [ ] These changes do not require tests because _____

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tests/wpt/mozilla/meta/mozilla/calc.html.ini

@@ -1,5 +1,8 @@
 [calc.html]
   type: testharness
+  [calc for border-width]
+    expected: FAIL
+
   [calc for column-width]
     expected: FAIL
 

tests/wpt/mozilla/meta/mozilla/style_no_trailing_space.html.ini

@@ -0,0 +1,5 @@
+[style_no_trailing_space.html]
+  type: testharness
+  [Untitled]
+    expected: FAIL
+