Bug 1625385 [wpt PR 22485] - [css-flexbox] Move flex-item-contains-st…

…rict.html test to WPT, a=testonly

Automatic update from web-platform-tests
[css-flexbox] Move flex-item-contains-strict.html test to WPT

This CL moves flex-item-contains-strict.html test from
css3/css-flexbox to external/wpt/css/css-flexbox with WPT
styles, adding links to the relevant specs, a proper title,
and test description.

Bug: 1063749
Change-Id: I5559de07cc72a44a36ed39c951562a156dfeabca
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2123695
Reviewed-by: Robert Ma <robertmachromium.org>
Reviewed-by: David Grogan <dgroganchromium.org>
Commit-Queue: Gyuyoung Kim <gyuyoungigalia.com>
Commit-Queue: Robert Ma <robertmachromium.org>
Cr-Commit-Position: refs/heads/master{#754029}

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wpt-commits: 1d7656ff988d83460ee4d120b8aaa2ceb6edb53f
wpt-pr: 22485

UltraBlame original commit: 27eff5d8ef1a36ab6c40222ae74c7842568b7c48