Resolve "Move EE differences for `app/assets/javascripts/notes/components/note_form.vue`"

What does this MR do?

Moves all EE differences for app/assets/javascripts/notes/components/note_form.vue into a mixin in the EE Directory

CE Backport: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/27824

Does this MR meet the acceptance criteria?

Conformity

• Code review guidelines
• Style guides
• Separation of EE specific content

Performance and testing

• Tested in all supported browsers

Closes #9971 (closed)