FEATURE: New share topic modal (PR #12804)

The share topic modal used to host both share and invite functionality. The new modal can be used only for sharing and has a link to invite.


Nitpick: Since it’s just one property you’re better off with this.set

        instructions: "Share a link to this topic:"
          instructions: "Notify the following users about this topic:"
            one: "Successfully notified %{username} about this topic."
            other: "Successfully notified all users about this topic."