Themes: Set a max-width on screenshots so they don't get blurry at very wide screen widths.

props matveb.
fixes #26172.

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Add back CSS rules for RTL resize handles.

Disable CSSJanus' swapLtrRtlInUrl option, as we currently don't use it otherwise (and it breaks this if left on).

props ocean90.
fixes #26449.

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git-svn-id: http://core.svn.wordpress.org/trunk@26620 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Inline documentation fixes for `wp_heartbeat_set_suspension()`.

See #25073.

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git-svn-id: http://core.svn.wordpress.org/trunk@26621 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Ensure that disabled select elements are distinguishable from normal ones. Fixes #26456, props TobiasBg.


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Core updates: Explicitly call wp_cache_delete() after a DB upgrade, as not all cache backends allow the entire backend to be flushed.

props dd32.
fixes #26173.

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git-svn-id: http://core.svn.wordpress.org/trunk@26623 1a063a9b-81f0-0310-95a4-ce76da25c4cd