Move branches dropdown to gl-dropdown [RUN ALL RSPEC] [RUN AS-IF-FOSS]

What does this MR do?

This replaces the existing dropdown in the branches page to GlDropdown

#263191 (closed)

Screenshots (strongly suggested)

Before	After

Search now is a gitlab-ui based component

Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
  • [-] I have included a changelog entry.
  • I have not included a changelog entry because this is behind a feature flag.
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content