Checklists are pasted / restored without checkboxes

### Expected
1. If the user copies a checklist to a clipboard, the paste result should be the exact copy of a checklist.
2. If the user deletes the checklist, and uses `Undo`, the checklist should be restored correctly

### Observed
In both cases mentioned above, only the text is pasted/restored, but not the checkboxes. Example video for the case of `Undo`:

https://user-images.githubusercontent.com/73365754/128861954-7d071bc2-8de3-464c-9413-f59c3d235643.mp4

### Reproduced
1. Have a note with checklist
2. Select the checklist and Cut (Delete) it
3. Paste (Undo) ~> only the text is pasted (restored), but not the checkboxes.

Device Make: Samsung Galaxy
Device Model: A31
Android Version: 10
Simplenote Version: 2.19-rc-1

Reproduce the issue on Android with a note containing a checklist, then trace the Cut/Paste and Delete/Undo entry points involved in restoring note content. Done means both clipboard paste and Undo restore the checklist text together with its checkboxes.

Written by the indexing model from the issue text.