To be able to disable jQuery Migrate as step 3 of updating the jQuery version shipped with WordPress, all `JQMIGRATE` warnings in the browser console will have to be addressed.
This includes many minor adjustments to a wide array of core files.
Follow-up to:
* Step 1: Disabling jQuery Migrate 1.4.1 in WordPress 5.5: [48323], [48324]
* Step 2: Updating jQuery to 3.5.1 and adding jQuery Migrate 3.3.x in WordPress 5.6: [49101], [49338], [49615], [49649]
Props Clorith, azaozz.
See #51812.
Built from https://develop.svn.wordpress.org/trunk@50001
git-svn-id: http://core.svn.wordpress.org/trunk@49702 1a063a9b-81f0-0310-95a4-ce76da25c4cd
9f12d7f575