Generic chooser views

Introduce a wagtail.admin.views.generic.chooser module to serve as a common base implementation for chooser modals. This can be loosely based on wagtail-generic-chooser but should incorporate improvements as outlined in https://github.com/wagtail/wagtail-generic-chooser/issues/44: in particular, using the table UI component for listing views, and using ‘partial’ HTML fragments for the browser results view and ‘create’ form submission so that we aren’t re-rendering the whole modal.

Acceptance criteria:

• A documented base set of views exists in wagtail.admin.views.generic.chooser (#8662)
• A documented viewset exists in wagtail.admin.viewsets.chooser (#8662)
• A base chooser widget implementation is provided and documented (#8662)
• A base StreamField chooser block is provided and documented (#8820)
• The page chooser mechanism inherits from this base implementation
• The image chooser mechanism inherits from this base implementation (#8778, #8804)
• The snippet chooser mechanism inherits from this base implementation (#8711, #8717)
• The document chooser mechanism inherits from this base implementation (#8776, #8777)
• A basic chooser for an arbitrary model can be implemented with minimal new code - simply extending the base viewset/widget class and specifying the model as an attribute (#8662)
• New instances can be created through the chooser view (#8726)
• The listing view uses the wagtail.admin.ui.tables component (#8662)
• Listings are searchable (where the model provides this) (#8669)
• Listings are filterable via django-filters filters
• Data sources other than models (e.g. django-rest-framework API endpoints) can be used (#8855)
• Where custom logic is common to chooser modals and widgets (e.g. converting an object ID to a dict representation that can be used for widget rendering), code is shared between them

[gasman]

@lb- Yep, the plan is to deprecate wagtail-generic-chooser - so yes, reviewing those open issues is a good plan. From a quick scan through the list, there’s a mix of things I hope to address in the rewrite (better filtering via django-filters, cleaner API for DRF data sources) and more general wishlist items that are probably a better fit for the Wagtail project anyhow (multiple selection, generalised link choosing).

[phildexter]

1. We can choose basic Snippets using the new chooser (from the chooser widget or a streamfield block).
2. We can create a new Snippet through the new chooser (from the chooser widget or a streamfield block).
3. We can search for a Snippet through the new chooser (from the chooser widget or a streamfield block).
4. We can filter objects through the new chooser.
5. We can do 1-4 for documents.
6. We can do 1-4 for images.
7. We can do 1, 3 and 4 for pages.
8. We can do 1-4 for sources other than models stored within the Wagtail DB
9. Documentation on how to extend