Bug 1665865 [wpt PR 25617] - [mathml] Implement special drawing of largeop operator...

Bug 1665865 [wpt PR 25617] - [mathml] Implement special drawing of largeop operator in displaystyle, a=testonly

Automatic update from web-platform-tests
[mathml] Implement special drawing of largeop operator in displaystyle

This implements special drawing of largeop <mo> element in display style
as described in step 3. of [1]. A new algorithm is introduced for that
purpose and in particular only used for <mo> elements that are made of
a single glyph. Existing painting logic for stretchy radical symbol is
reused and adapted to work with largeop operators.

[1] https://mathml-refresh.github.io/mathml-core/#layout-of-operators

Bug: 6606
Change-Id: Icca70f4bf464417809970fecc101e5aa7f149621
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2414298
Commit-Queue: Rob Buis <rbuis@igalia.com>
Reviewed-by: Koji Ishii <kojii@chromium.org>
Reviewed-by: Frédéric Wang <fwang@igalia.com>
Reviewed-by: Ian Kilpatrick <ikilpatrick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#819855}

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wpt-commits: 849c93ccec0cf5fcfbd641d003639be851c51c45
wpt-pr: 25617