Language Pack Upgrader: Allow to disable asynchronously translation updates.

* Don't touch VCS installs.
* Use the `async_update_translation` filter (which corresponds exactly to `auto_update_translation`) to entirely disable it, or based on the update offer. 

props nacin, ocean90.
fixes #28571.
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Restore the post type's view_item label for preview links that don't submit the changes.

fixes #28350.
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4.0-RC2.

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Modals: Remove yet more cruft that was causing unwanted coloration of icons.

props celloexpressions.
fixes #29147 (for real this time).

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Editor expand: revert back to scrolling to the editor top when switching Visual to Text, fixes #29338
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4.0-RC3.

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Add 'Release Lead' string to credits. see #29494.

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