Dexterity control panel endpoint should be renamed

[robgietema]

The dexterity control panel call is currently: https://demo.plone.org/++api++/@controlpanels/dexterity-types. Since dexterity is an implementation detail it should not be part of the url. My suggestion: https://demo.plone.org/++api++/@controlpanels/types.

[davisagli]

I suggest content-types rather than types.

This is a backwards-incompatible change so we would need to do it step by step:

1. Add support for the new name here and in Nick.
2. Update Volto to use the new name.
3. Deprecate the old name.