Split, refactor, simplify Form and block form editing components

[tiberiuichim]

We've started some work in making a more simplified version of Form.jsx, right now it's a reusable component in the @eeacms/volto-blocks-form addon.

Ideally I'd like to see the following structure:

• Form - used by Edit, makes use of metadata form and BlocksForm
• BlocksForm - only the "visual" form, split out of Form. It can only edit blocks. This would be a reusable component that can be used in other blocks, such as a "tabs block" or a "columns block" or a "section block". We already have addons like this built on top of this
• The drag/drop part would be extracted as a separate reusable component.
• All block manipulation bits and buttons should be separate to a "Edit block wrapper" component, so that it can be passed and customized as needed. I see here as candidates: drag handler, block delete button and the block mutation
• the block mutation (chooser) should be extracted from the Text block and moved to the Edit block wrapper.

[tiberiuichim]

Would be partially closed by #1826