Remove remaining Heartbeat API experimental notices

Props DH-Shredder.
Fixes #28626.

Built from https://develop.svn.wordpress.org/trunk@28872


git-svn-id: http://core.svn.wordpress.org/trunk@28672 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Perform a canonical redirect for posts that are published but are visited at a `?p=123&preview=true` URL.

Props amit, joostdevalk.
Fixes #20496.

Built from https://develop.svn.wordpress.org/trunk@28874


git-svn-id: http://core.svn.wordpress.org/trunk@28673 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Remove obsolete `wp_cache_delete('get_pages', 'posts')` from `clean_post_cache()`.

Fixes #27459.

Built from https://develop.svn.wordpress.org/trunk@28875


git-svn-id: http://core.svn.wordpress.org/trunk@28674 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Make the posts list table mode a sticky user setting. props garyc40, azaozz, ericmann. fixes #16774, #20335.

Built from https://develop.svn.wordpress.org/trunk@28876


git-svn-id: http://core.svn.wordpress.org/trunk@28675 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Fix the spacing between the wp-pointer arrow and bubble in LTR and RTL.

Fixes #28062.


Built from https://develop.svn.wordpress.org/trunk@28877


git-svn-id: http://core.svn.wordpress.org/trunk@28676 1a063a9b-81f0-0310-95a4-ce76da25c4cd