Triggering keyup will re-render the dropdown which is not needed when option persistWhenHide is true

This was re-rendering the dropdown unnecessarily

We need to update the results right away when we do bulk assignment.

1. Don't use instance variables, use `let` instead.
2. Add descriptions for all specs.
3. Share variables where possible.
4. Give labels more vivid names than 1, 2, and 3.
5. Remove deprecation warnings by passing issue IDs as '1,2,3' instead
   of an array, as that's how they're passed by the front-end. (The
   deprecation warning is for passing a nested array, which is what
   happens if an actual array is passed, as:
     `[1, 2, 3].split(',') == [[1, 2, 3]]`

The spritesheet should only load when an award emoji picker is opened.

This makes sure that the emoji spritesheet is loaded **only** when the emoji picker is opened. This saves 250-650KB on every page load.

Prevents !3785 from reverting the fix from !3449.

cc: @jschatz1 @zj @fatihacet 

See merge request !4469

Remove unnecessary vendor prefixes for browsers we no longer support.

Pretty simple, just removes a few prefixed properties for browsers we don't support.

See merge request !4368