jQuery UI 1.14.2; IE and Edge Legacy dropped

WordPress 7.1 includes an update to the latest stable version of jQuery UI, 1.14.2 from version 1.13.3. This update drops support for all versions of Internet Explorer & Edge Legacy which is inline with the WordPress Browser Support Policy.

This update sets jQuery.uiBackCompat to be equal to true to ensure that code written for the jQuery 1.11 API continues to function as expected. Additionally, $.fn._form, $.ui.ie, $.ui.safeActiveElement, and $.ui.safeBlur have been removed. WordPress core does not use any of these functions, but you should check your code and update it accordingly if it does.

See [62747] for the specific changes and #62757 for more background information.

props @masteradhoc and @joedolson for review

#7-1, #dev-notes, #dev-notes-7-1, #external-libraries