Move jQuery GL Dropdown to commons.

What does this MR do?

Moves gl dropdown MR to EE.

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

No

Why was this MR needed?

ee branch for move gl

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
• If paid feature, have we considered GitLab.com plan and how it works for groups and is there a design for promoting it to users who aren't on the correct plan

What are the relevant issue numbers?

#38869