Align source contexts

Problem/Motivation

UI Patterns 2

UI Patterns 2 is shipped with those context for sources:

The mix between context_definitions and context_requirements is a bit complex, and some context_requirements naming are too specific (field_formatter for example).

There are some plans to add a "Content" context (not the same as "Content entity" for sources which can be stored only in a content field (for Layout Builder overrides or Ckeditor5 for example): #3501797: Add a ContentEntity source for slots with a Content entity context

Display Builder

The module doesn't use context_definitions and has those context_requirements:

• is_display_builder_views. Example: ViewExposedSource
• is_display_builder_page_layout. Example: PageTitleSource

Those contexts don't tell about where we are in the Drupal API, what we have access from the source, but about the specific Display Builder sub-module using it. So, they sources will not be compatible with the UI Patterns 2 ecosystem and the future Display Builder ecosystem.

In a perfect world, Display Builder will have no Source plugins in its codebase.

Proposed resolution

Instead of is_display_builder_views, use the ones already defined and managed by UI Patterns 2.

Instead of is_display_builder_page_layout . Add a "Page" context which will be able to be proposed for UI Patterns 2 inclusion. See #3529737: Add proper page management

The future Content context from UI Patterns 2 must follow the same principles because it will also be used in Display Builder Entity View's overrides. We can implement it first in Display Builder.

If it is the opportunity to propose a backward compatible simplification to UI Patterns 2 team, let's do it.