Bug 1624143 [wpt PR 22381] - Update MathML tests for embellished operators., a=testonly

Automatic update from web-platform-tests
Update MathML tests for embellished operators. (#22381)

This commit updates tests after [1] [2]:

* merror, mprescripts, none, unknown are now treated as other mrow-like
  elements.
* maction and semantics are moved into a separate file and new tests
  added now that they are mrow-like elements with some hidden children.

[1] w3c/mathml#182
[2] w3c/mathml#183
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wpt-commits: c38ae4ac2e0af285deb06f33c75e1699d0718942
wpt-pr: 22381

UltraBlame original commit: 8e8fe19364e1c1ddc7d7ce589aa2fd8d8e23572c

Author: marco-c