"Comments on prior version" modal and emoticons menu z-index issue

Steps to reproduce

1. Have some commit/pr with comments on a certain section
2. Refactor the section so that comments disappear
3. Check “Comments on prior versions” feature
4. Modal opens
5. Try to reply to some of the comments so that text editor opens
6. Try to open Emoji menu

Expected

Emoji menu displays on top of the “Comments on prior versions” modal

Actual

Emoji menu is displayed underneath.

Reason

Obvious one. Incorrect z-index of the Emoji popup menu.