[2.0.0-alpha3] Blocks: Add sources with an entity context

Entity Field Source Plugin (for slots): Pick and configure a block from all field specific to the entity related to the display we are currently editing. Form : select the field, a formatter and configure the formatter.

This look like a generalization of the FieldFormatter source from ui_pattrns_field_formatters where the context is the (entity type, field) tuple (we cannot select something outside of the field we are currently working on):, and the configuration is the selected formatter configuration form

An other issue is dealing with the generalization of an ui_pattrns_field_formatters source plugin: ✨ [2.0.0-alpha3] Add allow_expose source plugin Active

i take this one :)

This can easily done with the refactoring of the forms. We can use slot form widget inside a block and we are done. Should I take it?

An we exchanged during the weekly, let's remark the following thing in the current 2.0.x codebase.
when we treated the issue 3444716 ✨ [2.0.0-alpha3] Add block source (for slots) Fixed ,
we declared a new consumer "ui_patterns" for block discovery and filtering.
As seen in Drupal\ui_patterns\Plugin\UiPatterns\Source::listBlockDefinitions,
we are calling plugin.manager.block:getFilteredDefinitions with ui_patterns as the first argument.
(see Drupal\Core\Plugin\FilteredPluginManagerTrait::getFilteredDefinitions).
this implies, some alter hooks are called during plugin discovery "plugin_filter_{$type}" and "plugin_filter_{$type}__{$consumer}".

We proposed a first implementation of those hooks in ui_patterns.module, and this may not be perfect right now,
and has to refined maybe in this issue.

see functions "ui_patterns_plugin_filter_block__ui_patterns_alter" and "ui_patterns_plugin_filter_block_alter" in ui_patterns.module

thanks christian, to parallelize last alpha3 efforts, i re-take it :)

Entity Link Label Source Plugin (for strings): Select the entity link among $entity_type->getLinkTemplates()

Removed from scope

ready for review

I will have a look