No Access to Layout Builder Local Contexts

Problem/Motivation

I want to be able to add custom contexts based on the $entity. When rendering an entity in Full view mode, custom ContextProviders can pull the entity from the route. But, what if you are working with a view of entities in Teaser view mode? I don't see a way to inform a ContextProvider of the entity.

Steps to reproduce

Proposed resolution

Add a new hook like hook_layout_builder_local_context_alter(&$contexts, $entity, $display). I would add it to the method below. Layout Builder uses this method to define the contexts when rendering an entity's layout. It:

1. receives $entity as a parameter
2. generates contexts based on local data
3. runs all the contexts from ContextProviders

// from .../core/modules/layout_builder/src/Entity/LayoutBuilderEntityViewDisplay.php

  /**
   * Gets the available contexts for a given entity.
   *
   * @param \Drupal\Core\Entity\FieldableEntityInterface $entity
   *   The entity.
   *
   * @return \Drupal\Core\Plugin\Context\ContextInterface[]
   *   An array of context objects for a given entity.
   */
  protected function getContextsForEntity(FieldableEntityInterface $entity) {
    $available_context_ids = array_keys($this->contextRepository()->getAvailableContexts());
    return [
      'view_mode' => new Context(ContextDefinition::create('string'), $this->getMode()),
      'entity' => EntityContext::fromEntity($entity),
      'display' => EntityContext::fromEntity($this),
    ] + $this->contextRepository()->getRuntimeContexts($available_context_ids);
  }

I can take a first pass at making the change. I'd appreciate some feedback first. Is there already a way to modify the local contexts that I just haven't thought of?

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet