ci: add e2e ests for editor toolbar buttons

[jasonbahl]

This PR adds tests for the editor toolbar buttons. This tests behavior of the buttons before the buttons have been refactored to be pluggable via 3rd parties to ensure that behavior that works before the refactor also continues to work after.

• introduce getCodeMirrorValue util function
• add tests for all the toolbar buttons
  • [x] Toggle Auth Button
  • [x] Prettify
  • [x] Copy
  • [x] Merge Fragments
  • [x] Share