Buildable plugins bypass their own dependency injection

Problem/Motivation

DisplayBuildableInterface extends ContainerFactoryPluginInterface, and DisplayBuildablePluginBase::create() already injects entity_type.manager, current_user and module_handler. None of the four buildable plugins used them. They reached for the container statically, and resolved their entity in the constructor with EntityViewDisplay::load(), PageLayoutEntity::load() or View::load().

The cause is ordering: create() does new static(...) first and assigns the services after, so nothing the constructor needs can be injected. Each constructor carried a "No dependency injection in plugin constructors" comment, which describes the problem rather than justifying it.

This matters beyond tidiness: a contributed module writing its own integration will open EntityView and copy it. It is the reference implementation whether we call it that or not.

Proposed resolution

• Constructors resolve nothing. They only normalize ::$configuration, keeping the identifier the plugin was built with and stashing an object the caller passed in.
• Each plugin resolves lazily through $this->entityTypeManager: EntityView::getDisplay(), EntityViewOverride::getDisplay() and ::getField(), PageLayout::getEntity(), ViewDisplay::getExtender().
• Extra services come from an overridden create() that calls parent::create() and assigns on the result: sampleEntityGenerator, dataConverter, time, displayBuildableManager, currentPath, pluginCacheClearer.
• Removed the seven lazy \Drupal::service() accessors in EntityViewOverride and PageLayout, plus EntityViewOverride::entityTypeManager(), which shadowed the injected property and had no callers.
• The base create() docblock now documents the extension pattern and why a constructor must not resolve its display.

Every remaining call sits in a static method the interface mandates: collectInstances(), checkAccess(), getUrlFromInstanceId() and their static helpers. Those have no $this to inject into and cannot be fixed without changing the contract. Nothing in instance context reaches for the container.

Remaining tasks

• Review.

User interface changes

None.

API changes

PageLayout::$entity was public and is now protected, read through ::getEntity(). It had no callers outside the plugin. Everything else is protected or private internals. Plugin IDs, stored configuration keys, DisplayBuildableInterface and DisplayBuildablePluginBase::create() are unchanged.

Data model changes

None.