Sync web-platform-tests PR 25432 into mozilla-central (this bug is closed when the sync is complete).

PR: https://github.com/web-platform-tests/wpt/pull/25432
Details from upstream follow.

b'Fr\xc3\xa9d\xc3\xa9ric Wang <fwang@igalia.com>' wrote:

[mathml] Add a web platform test for MathML in content-editable div

This CL adds a web platform test to check that MathML content inside a
content-editable div is still correctly laid out. It is inspired from
the similar tests mathml/relations/html5-tree/integration-point-4.html
and mathml/relations/css-styling/multi-column-layout.html for SVG
embedding and fragmentation respectively. Currently, this test passes
with EditingNG enabled.

Bug: 6606, 1125133, 707656
Change-Id: I1bac091ca02608891e2d36e34c0a8190c40506be
Reviewed-on: https://chromium-review.googlesource.com/2398481
WPT-Export-Revision: f9fd07f51d5620e73016c96b47d0c00e930dd2cb

CI Results

Ran 12 Firefox configurations based on mozilla-central, and Firefox, Chrome, and Safari on GitHub CI

Total 1 tests and 2 subtests

Status Summary

Firefox

OK : 1
PASS: 2

Chrome

OK : 1
PASS: 2

Safari

OK : 1
PASS: 2

Links

Gecko CI (Treeherder)
GitHub PR Head
GitHub PR Base