Make name content attributes consistently atoms and put them in rare_data for fast access
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All codepaths setting the name content attribute now use an atom, which is also stored in rare_data for direct lookup by a get_name method.
Paralleling the get_name method, I added a get_id method, which makes some internal id-lookup cases nicer.
A new test tests for a name setter on every HTML element type. In addition to its overt and upstreamable purpose of checking IDL property reflection semantics, for us this test also hits some Servo assertions that make sure the name is an atom in every case. If the test doesn't crash, even a failed test case still has the attribute as an atom rather than some other type. The failed cases are for elements that we have unimplemented or completely stubbed; I added a few missing name IDL properties to otherwise implemented elements.
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Implement "translate" attribute
This attribute is almost a straightforward enumerated one, but the getter value inherits from parents when the content attribute is absent, even when the parents are non-HTML elements. This initial commit is using LocalName::from on a static string; once html5ever has a release with "translate" in the built-in local name list, a small change will be needed.
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style: sync changes from mozilla-central
See each individual commit for details. This also cherry-picks #23463 with a few fixes that were needed in Gecko-only code.
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Remove unused code (3/N)
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Third PR in a series of PRs to remove unused/dead code from servo, powered by an (upcoming) tool of mine. Please take a look and tell me if you want to keep something.
* First PR: #23477
* Second PR: #23498
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