codeintel: Extra "Find implementations" button

Created by: chrismwendt

Sometimes multiple "Find implementation" buttons appear in the hover popover. No consistent repro steps have been identified, but we have some evidence that it actually occurs:

Visit https://sourcegraph.com/github.com/sourcegraph/sourcegraph@5fd162fc3939d36853dd58e26c6adee1955bfa46/-/blob/cmd/frontend/internal/auth/userpasswd/config.go?L14:6

Extensions running when it occurred:

My first guess is that there's a race condition somewhere in the extension host.