servo: Merge #14535 - Introduce a PropertyId enum and use it instead of strings of property names (from servo:property-id); r=mbrubeck

<!-- Please describe your changes on the following line: -->

* `LonghandId` and `ShorthandId` are C-like enums
* `Atom` is used for the name of custom properties.
* `PropertyDeclarationId` is the identifier for `PropertyDeclaration`,
  after parsing and shorthand expansion. (Longhand or custom property.)
* `PropertyId` represents any CSS property, e.g. in CSSOM.
  (Longhand, shorthand, or custom.)

CC upsuper

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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
- [ ] These changes do not require tests because _____

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Source-Repo: https://github.com/servo/servo
Source-Revision: 6dd4b4822fa788694153ee61a04dd9a5dfb748ec

UltraBlame original commit: daaa89ca8da2cf8fa5142c69ba50bcf12b306204

Author: marco-c

servo/Cargo.lock

@@ -32,36 +32,6 @@ datetime
 local
 number
 dir
-bottom
-top
-left
-right
-width
-height
-margin
--
-bottom
-margin
--
-top
-margin
--
-left
-margin
--
-right
-padding
--
-bottom
-padding
--
-top
-padding
--
-left
-padding
--
-right
 DOMContentLoaded
 select
 input