Rich text singletons set to `readOnly` still seem editable

[abea]

To Reproduce Steps to reproduce the behavior:

1. Create a piece type with a rich text singleton in its schema. Set that singleton field to readOnly: true.
2. When editing a piece of that type, go to that field and click to "Add Rich Text."

Expected behavior There should not even be a button to add the singleton widget. You should not be able to interact with the area there.

Describe the bug Singleton (and likely area) fields in editor modals do not reflect "read-only" status in the UI. When you put content in there it will not save, but it seems from the editor's point of view that it should.

[abea]

This also seem to be the case for array fields. A full review of field types might be in order.