[META] Remove jQuery UI components used by Backdrop core and replace with a set of supported solutions

[klonos]

This is the respective issue for https://www.drupal.org/project/drupal/issues/3067261 and related to #4349:

Problem/Motivation

JQuery UI was added as a dependency for Drupal core 10 years ago to improve our UX. Since then majority of the frontend community has moved on to using other libraries. For that reason, JQuery UI has been having trouble attracting new maintainers, and has been unmaintained since 2017 as announced by one of the maintainers of the project in this blog post. The most recent release was published in 2016 and there's no one responding to PRs in their Github repository.

In the meantime the former jQuery foundation became the JS foundation which merged with Node's foundation and formed OpenJS Foundation. That lists jQuery UI as an Emeritus project in https://openjsf.org/projects/ which is described as:

Emeritus projects are those which the maintainers feel have reached or are nearing end-of-life

https://www.drupal.org/project/drupal/issues/3051352 provides a plan for libraries that are unused.

[alanmels]

This is just to update there is an initiative to replace JQuery with vanilla Javascript in Drupal's core: https://www.drupal.org/project/drupal/issues/3052002

Also nice material is on https://www.outsideonline.com/2353261/how-we-removed-jquery-our-drupal-7-site#close