Give interface-typed entities magic field properties

[mglaman]

Closes #1048. First slice of #929, scoped to ContentEntityInterface. Type inference fix.

What changed

A parameter typed ContentEntityInterface, NodeInterface, or any other interface extending ContentEntityInterface now gets the same magic field properties as a concrete entity class. Before, $entity->field_foo on such a value was reported as an undefined property while the same access on a Node worked.

Two layers needed fixing:

• The extension's checks were false for the interface itself. EntityFieldsViaMagicReflectionExtension used implementsInterface() and EntityFieldReflection used isSubclassOfClass(). Both are false when the reflected class is the interface. Both now use is(), the same change Align legacy rules and reflections with current PHPStan API conventions #1027 made for FieldItemListInterface.
• PHPStan never asked the extension about interfaces. PHPStan only consults property reflection extensions for a class that allows dynamic properties, which means a __get() declaration, an #[AllowDynamicProperties] attribute, a @phpstan-require-extends tag, or membership in universalObjectCratesClasses. Entity interfaces have none of these. extension.neon now lists Drupal\Core\Entity\ContentEntityInterface as a universal object crate, which matches every interface extending it. That is an honest description: ContentEntityBase::__get() accepts any property name.

EntityFieldReflection no longer needs a ReflectionProvider, so the extension's constructor no longer takes one.

Why not @phpstan-require-extends

A stub with @phpstan-require-extends ContentEntityBase opens the gate for ContentEntityInterface only. For NodeInterface, PHPStan then resolves properties through the required class before consulting the interface's own @property tags, and $node->book lost its BookData type. The crate list opens the gate for the interface hierarchy itself, so the annotations extension runs first and @property tags keep winning.

Side effects worth knowing

• @property tags on entity interfaces now resolve. NodeInterface::$book and a project's own @property string $custom on an interface extending ContentEntityInterface were undefined-property errors before. This is a strict improvement.
• With entityFieldsViaMagicReflection: false, entity field access is mixed instead of an undefined-property error. The crate registration is what opens the gate, and the crate extension is the fallback when ours is off. The README note under "Disabling extensions" documents this.

Testing

Unit cases for hasProperty() on ContentEntityInterface (true) and EntityInterface (false), and getProperty() on ContentEntityInterface. Fixture cases for field_myfield and original on a ContentEntityInterface parameter and field_myfield on a NodeInterface parameter. The existing book-module fixture guards the @property precedence. Full suite, self-analysis, and phpcs are green.

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