External Libraries: First pass at fixing jQuery deprecations in WordPress core and bundled themes.

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.

git-svn-id: https://develop.svn.wordpress.org/trunk@50001 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/export.php

@@ -29,7 +29,7 @@ function export_add_js() {
 		var form = $('#export-filters'),
 			filters = form.find('.export-filters');
 		filters.hide();
-		form.find('input:radio').change(function() {
+		form.find('input:radio').on( 'change', function() {
 			filters.slideUp('fast');
 			switch ( $(this).val() ) {
 				case 'attachment': $('#attachment-filters').slideDown(); break;