This updates the various resources to support fine-grained setting of

text types per-field, to list the text types, and to optionally return

the raw values along with the forced values (if using force-text-type=

and include-raw-text-fields=).
Support for setting text_type= is still allowed on the resources that

have split this field out. It will act as if individual *_text_type=

values were passed. However, the returned text_type value in the payload

is now hard-coded to null.
New text.per_field_text_types and text.can_include_raw_values

capabilities have been added.
This is part of a set of changes to allow for per-field optional for

Markdown. It requires the other set of changes.

Unit tests pass.
Tested all the new support through the UI, using upcoming changes.