In `wp_update_term()`, limit duplicate slug checks to the same taxonomy as the updated term.

In 4.1 [30240], `wp_insert_term()` was modified to allow the creation of terms
with duplicate slugs, as long as the terms are in different taxonomies.
`wp_update_term()` didn't get the corresponding modification, with the result
that term updates fail when the term being updated shares a slug with an older
term, regardless of that older term's taxonomy.

Props ipm-frommen.
Fixes #30780 for trunk.
Built from https://develop.svn.wordpress.org/trunk@30985


git-svn-id: http://core.svn.wordpress.org/trunk@30971 1a063a9b-81f0-0310-95a4-ce76da25c4cd
TinyMCE wpView: when clicking on the Edit button, move the focus back to the editor before opening the modal. This is needed for IE so TinyMCE can save the proper DOM "bookmark", and makes it possible to move the focus to the modal after it is opened.
See #30817.
Built from https://develop.svn.wordpress.org/trunk@30986


git-svn-id: http://core.svn.wordpress.org/trunk@30972 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Customizer: Improve IE 8 compatibility.

* Use square bracket notation for `default` keywords.
* Use Underscores `indexOf` for arrays.

props westonruter, ocean90.
fixes #30781 for trunk.
Built from https://develop.svn.wordpress.org/trunk@30991


git-svn-id: http://core.svn.wordpress.org/trunk@30973 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Customizer: Use correct event variable when moving widgets to another widget area. 

Fixes "ReferenceError: event is not defined error." in Firefox.

props tywayne.
fixes #30818.
Built from https://develop.svn.wordpress.org/trunk@30992


git-svn-id: http://core.svn.wordpress.org/trunk@30974 1a063a9b-81f0-0310-95a4-ce76da25c4cd