Make MathML boolean attributes ASCII case-insensitive.
This commit ensures MathML boolean attributes (namely displaystyle,
mo@stretchy, mo@symmetric, mo@largeop, mo@movablelimits,
munder@accentunder, mover@accent, munderover@accent,
munderover@accentunder) are ASCII case-insensitive [1]. For
displaystyle that was handled in [2]. For mover/munder/munderover
attributes, this is covered by a test case from scriptlevel-001.html
checking both case-insensitivity and dynamic changes at the same time ;
the latter still seems broken, so these checks are moved into separate
test cases. For mo attributes, a new WPT test is added. Note that
mo@accent, mo@fence, mo@separator are not part of MathML Core (with the
two last without visual effect), we make them case-insensitive for
consistency but don't bother adding tests for them.
[1] https://w3c.github.io/mathml-core/#dfn-boolean used here:
[2] https://bugzilla.mozilla.org/show_bug.cgi?id=1574087
Differential Revision: https://phabricator.services.mozilla.com/D218944
bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1912435
gecko-commit: 7e71291be84261d2df2606da19bc61ac14f6c207
gecko-reviewers: emilio