Consolidate (or formalize standards for) multiple places to perform a Merge Request "Reopen" action

When a merge request is closed and an authenticated user is viewing the page, there are three separate ways to reopen that merge request.

Top "kebab"	Closed Widget	Comment Box

While this is very convenient, it may be more trouble than it's worth.

One notable difference already: The Comment Box button is the only one that disappears when the user is authenticated but doesn't have the right authorization to reopen the MR.

We should choose a path forward.
Some potential options (non-exhaustive):

• Define an acceptable list of places actions like this should appear
• Document some guidelines around "duplicating" existing behaviors
• Require that a given action is only ever in one place on the MR page