Media grid: Don't show a misleading message for an empty library.

This uses the existing string from the list table. We should revisit a better overall experience for the two situations (empty library vs. search with no results) in 4.1.

props voldemortensen.
fixes #29404.

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Editor expand:
- Adjust calculation when comparing sidebar position to wpfooter top. Fixes an annoying jumping when the user scrolls off the bottom.
- Use a var for the 'bottom' distance of the sidebar.
- Fix sidebar pinning when it's height is nearly the same as the viewport height.
Fixes #29349
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TinyMCE: fix the 'tabfocus' plugin to check if default is prevented on pressing tab, bind the events later so other plugins can cancel them. Merged upstream in https://github.com/tinymce/tinymce/commit/86098b348582e1544cc208db25954d31755e6d13 together with another change.
Fixes #29430
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Query: Add comment to the parse_tax_query() method reflecting [28987].

see #28739.

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Media: Translate a string for the search placeholder.

props alex-ye.
fixes #29448.

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Media: add a class to the <script> tag for the JSON encoded playlist data so it can be easily selected in WPPlaylistView. Props SergeyBiryukov, fixes #29383
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Avoid PHP notices when checking for local requests in in WP_Http.

props markoheijnen.
fixes #29392.
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Comments: Simplify JS for inline edit and reply.

fixes #27533.

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Canonical: Apply redirects to HEAD requests too. Adjusts [28958].

props SergeyBiryukov.
fixes #27498.

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DB: Revert [28814] and require a WHERE for wpdb::update().

see #26106.

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Merge pull request #6 from WordPress/master

Update