Signed-off-by: NDmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

See https://github.com/stefanpenner/es6-promise/issues/100

```
[WDS] Warnings while compiling.
./vendor/assets/javascripts/es6-promise.auto.js
Module not found: Error: Can't resolve 'vertx' in
'/Users/eric/Documents/gitlab/gitlab-development-kit/gitlab/vendor/assets/javascripts'
 @ ./vendor/assets/javascripts/es6-promise.auto.js 140:16-26
 @ ./app/assets/javascripts/application.js
 @ multi (webpack)-dev-server/client?http://localhost:3808
./application.js
```

In an effort to tackle #18437 this removes 2 of the jQuery UI plugins. Highlight & autocomplete, both used once in our code. Highlight was just removed easily, autocomplete was replaced with GL dropdown

- Changes to use a single instance of timeago
- Uses one timeout for every element, rather than 1 per element

Closes #25728

Part of #18437 to remove jQuery UI. This removes the datepicker

Added test to replicate the bug, also added a couple of helpers that can be reused
on the testing suite to resize the browser window, these helpers are located on the
spec/support/mobile_helpers.rb

Fixed eslint failures

Adds changelog

account for merge request fixed affix bar when adjusting scroll targets

Moved most of the functions that contained "window.doSomething" that were located at:
- app/assets/javascripts/application.js
To the following file:
- app/assets/javascripts/lib/utils/common_utils.js

The functions listed here:
- window.ajaxGet
- window.split
- window.extractLast
- window.rstrip
- window.disableButtonIfEmptyField
- window.disableButtonIfAnyEmptyField
- window.sanitize
- window.unbindEvents
- window.shiftWindow

Now will be accessible from the "gl.utils" namespace