Bug 1821980 [wpt PR 39077] - [Gecko Bug 1821980] Update mathvariant W…

…PT tests. Bug 1821980, a=testonly

Automatic update from web-platform-tests
Update mathvariant WPT tests.

In MathML Core, the mathvariant attribute is now restricted to the mi
element and to value "normal". Some related WPT tests were updated in
[1]. This commit moves other tests assuming full mathvariant support
into our internal tests. It also tweaks some existing tests to only
rely on MathML Core features.

* mathvariant-basic-transforms-with-default-font.html: This test assumes support for italic, bold and bold-italic mathvariants so move it to internal tests.
* mathvariant-case-sensitivity.html: This one tests all mathvariant values, so move it to internal tests.
* mathvariant-double-struck-font-style-font-weight.html: This test assumes support for double-struck mathvariant so move it to internal tests.
* Other generated mathvariant-*.html tests for each value (other than "normal") are also moved to internal tests.
* direction.html: Remove use of mathvariant="bold" since this test is actually testing the dir attribute.
* presentational-hints-001.html: Verify that local author style for text-transform wins over presentation hints for mathvariant. Tweak it to use value "normal" on the mi element and text-transform: uppercase.
* presentational-hints-002.html: This is testing dynamic setting of mathvariant. Tweak it to use value "normal" on the mi element.

[1] web-platform-tests/wpt#38490

Differential Revision: https://phabricator.services.mozilla.com/D172871

bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1821980
gecko-commit: 1ea808cbf56afaf7a890319225b3c93d24726888
gecko-reviewers: emilio

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Align mathvariant implementation on MathML Core.

In MathML Core, the recommendation is to directly use the proper
character from the Mathematical Alphanumeric Symbols instead of the
mathvariant attribute. The exception is for automatic italicization on
single-char `<mi>` element. This is implemented via a new text-transform
value "math-auto" [1] which is the default on the `<mi>` element. The
mathvariant attribute is now restricted to that element and to value
"normal" in order to force upright text instead [2]. This CL implements
this restriction together with that new text-transform value under the
mathml.legacy_mathvariant_attribute.disabled flag.

Some legacy MathML cases where math-auto alone does not work are
still handled via MathMLTextRunFactory.

[1] https://w3c.github.io/mathml-core/#new-text-transform-values
[2] https://w3c.github.io/mathml-core/#the-mathvariant-attribute

Differential Revision: https://phabricator.services.mozilla.com/D172395

bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1821980
gecko-commit: 72da4ec089de56dc3c3cdb69e879b66b5fd3a3ab
gecko-reviewers: emilio, jfkthame

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wpt-commits: da2b6993b2e91a0b352e4a6650ca9d6565deb997, 1a2dcdf30e01fe1011d1127bd47653baf3b1484e
wpt-pr: 39077