Use jQuery objects in ref dropdown
## What does this MR do?
Keeps the behaviour the same as the ref dropdown, however it now uses jQuery objects to handle the HTML creation instead of passing strings around. It pretty much worked out the box so not much was changed in the dropdowns themselves. Will be easy to transfer this over to other dropdown menus as well.
cc. @jschatz1 @rspeicher @DouweM
Do we want this to go into a patch release?
See merge request !4850
Refs dropdown is now loaded async
## What does this MR do?
The refs dropdown is loaded async so not to block the page.
## What are the relevant issue numbers?
Part of #18202
## Screenshots (if relevant)

See merge request !4508
Fixed issue with enter key selecting wrong option in dropdown
If you search for a label and press enter the dropdown will select the last element rather than the first. This is because the currentIndex is -1 rather than 0

Closes#17630
See merge request !4210
If you search for a label and press enter the dropdown will select the last element rather than the first. This is because the currentIndex is -1 rather than 0
Closes#17630
Updated UI for new merge request
Closes#2540


See merge request !3228
Search Design fixes
Closes#14800
- Use colors according to design
- Fix width of search input


See merge request !3475
Dropdown arrow support
When the dropdown is open, you can scroll through the list of items with the up & down arrow keys. When an item is focused, the enter triggers the click event for that row.
Closes#14455
See merge request !3385
Fixes issue with dropdowns not selecting values
Fixes issue with dropdowns not selecting when navigating between tabs
Closes#14813
See merge request !3478
Location aware search
Closes#3400#14217
Introduces suggestion grouping on the search box and adds the ability to the user to remove the location to search on.
**Notes**
- Suggestions are now grouped by category.
- Suggestions are displayed when no location is set.
- Would be great to provide suggestions for the specified location which could be a project or group.
- A location is set from the server for projects/groups related urls.
**Default Apparence**

**When location badge is present**

**Suggestions**

**Suggestions when location badge is present**

Closes#3400
See merge request !3212