Move "Assign to commenting user" from comment actions to user popover

Problem to solve

In #191455 (closed) we added an "Assign to commenting user" action in the dropdown for issue comments, but there are some things we could change:

  • Moving it into the user popover
  • Add "issue" to the button text as object what this action refers to
  • Add the username to the button text to make the action more clear

I did a quick mockup to show how this could work, but it's not very aesthetically pleasing yet and might make this action too prominent.

Before After
image image

/cc @rayana @pedroms @mikelong @tauriedavis @jakeburden As you were all involved in the initial discussion around this.