Apply draft content more like Matrix fields

[timkelty]

With a Matrix field, multiple authors can work in multiple diverged drafts without worrying about overwriting each other, because the entries are all saved individually.

With the same field represented as a CKE field with nested entries, the field data is always replaced wholesale, with the applying draft winning any conflicts. This can result in unintentionally losing/overwriting changes.

Example use case:

• Entry 1 (canonical entry)
  • has a CKE field with a quote nested entry type
• User 1 is working on Draft 1 of Entry 1
• User 2 is working on Draft 2 of Entry 1
• User 1 applies Draft 1, correcting some typos
• User 2 applies Draft 2, adding a quote

When Draft 2 is applied, the edits applied from Draft 1 are lost.
With the same field represented as a Matrix, Draft 2 is updated as soon as Draft 2 is applied to the canonical entry.