Migrate Protected Branches access dropdown to Vue

The following component utilizes our old deprecated jQuery-based dropdown implementation and should be replaced with a new implementation based upon GitLab UI's GlDropdown component:

• app/assets/javascripts/projects/settings/access_dropdown.js, used in:
  • app/assets/javascripts/protected_branches/protected_branch_create.js
  • app/assets/javascripts/protected_branches/protected_branch_edit.js
  • (It is also used in: #284787 (closed)).
• app/views/projects/protected_branches/_create_protected_branch.html.haml
• app/views/shared/projects/protected_branches/_update_protected_branch.html.haml
• ee/app/views/projects/protected_branches/ee/_create_protected_branch.html.haml
• ee/app/views/projects/settings/ee/_access_level_dropdown.html.haml (Also shared with Protected Tags (see: #284787 (closed))

Instructions

Ith should be possible to migrate to app/assets/javascripts/groups/settings/components/access_dropdown.vue. However this is a little interesting as there is a big CE/EE split with the partials, but potentially a lot of this can be deleted thanks to this migration.

In this MR: !70208 (merged) the Access Dropdown for Protected Environments was migrated to the aforementioned Vue Component.

See also: Migrate Protected Tag access dropdown to Vue (#284787 - closed)