Pajamas migration GlDropdown in project_modal

What does this MR do and why?

This MR migrates legacy GlDropdown to GlCollapsibleListbox according to OKR

Resolves #421249 (closed)

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

Before	After
dropdown.mov	listbox.mov

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Go to project
2. Secure -> Policies
3. Open edit policy project in dropdown in top right corner
4. Dropdown will be in modal

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #421249 (closed)