Move gl dropdown

What does this MR do?

Moves GL Dropdown to commons jquery area and imports from there.

EE Version: https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/3830

Are there points in the code the reviewer needs to double check?

No

Why was this MR needed?

To check off gl_dropdown for https://gitlab.com/gitlab-org/gitlab-ce/issues/38869

Screenshots (if relevant)

None

Does this MR meet the acceptance criteria?

• Review
  • Has been reviewed by Frontend
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• Internationalization required/considered

What are the relevant issue numbers?

#38869 (moved)