State of the art for dropdown implementations - Roadmap to have one lib

The frontend code base has many dropdown implementations. We should collect the most common ones and document which of them can be used in future (and how) and which of them are discouraged.

This hopefully brings us closer to having one implementation at some point.

Possible Plan

1st: Document

Document current usage: https://gitlab.com/gitlab-org/gitlab-ce/issues/39998

2nd: List & Evaluate

List the usage of all dropdowns: https://gitlab.com/gitlab-org/gitlab-ce/issues/39996

3rd: Features

List all the features we need a dropdown to have: https://gitlab.com/gitlab-org/gitlab-ce/issues/39994

4th: Compare existing solutions

Compare existing solutions: https://gitlab.com/gitlab-org/gitlab-ce/issues/39997

5th: Remove!

After all the steps have been completed and backed with documentation and not personal opinions (which is the main blocker atm) we can start remove.

6th: End result

Ideally we would end up with

  1. One basic dropdown, like bootstrap, most of the places we use one we only need a simple <ul> with some <li>
  2. One advanced dropdown, like select2|gldropdown, for the API calls, etc
Edited by Inactive Account