Fix note flicker with note you can't edit and trailing new line edge case

What does this MR do?

1. Fix case causing flicker with trailing new line in updated note
2. Fix case causing flicker where we were comparing against nothing because .original-note-content was missing on notes that you couldn't edit.

Are there points in the code the reviewer needs to double check?

To reproduce previously:

With scenario 1.

1. Keep 2 tabs open with the same issue
2. On one of the tabs, edit a note and leave a trailing new line
3. Notice the note flickering whenever the polling endpoint was hit

With scenario 2.

1. As user1, create an issue and a note
2. As user2, navigate to the same issue
3. As user1, edit the note
4. Notice on user2, the note flickering whenever the polling endpoint was hit

Does this MR meet the acceptance criteria?

• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #32449 (closed)