Share frontend code between Protected Branches and Protected Tags feature

Overview

With addition of Protected Tags with !10356 (merged), there has been a lot of duplication of frontend code between Protected Branches and Protected Tag feature, this issue is intended to reduce duplication with following proposal;

Proposal

• Convert classes under protected_branches to pure ES6.
• Create shared JS classes under protected_refs, combining common properties between protected_branches and protected_tags.
• Create partials under app/views/shared/protected_refs which can be used across protected_branches and protected_tags.

Related Issues

#18193 (closed)

#18471 (closed)