[TypeDeclaration] Migrate EmptyOnNullableObjectToInstanceOfRector to NullableObjectToInstanceofFactory

[TomasVotruba]

Follow-up to #8633. That PR extracted NullableObjectToInstanceofFactory and migrated four rules, leaving EmptyOnNullableObjectToInstanceOfRector out because it built the instanceof target through StaticTypeMapper::mapPHPStanTypeToPhpParserNode() -> Name rather than FullyQualified(getClassName()).

For a plain nullable ObjectType (what this rule has after TypeCombinator::removeNull()), both paths resolve to the same fully qualified name, so the rule now uses the shared factory. This drops the StaticTypeMapper dependency and the instanceof Name guard.

Added aliased_import.php.inc to lock the one path where the two approaches could in theory diverge - an aliased import (use X as Y) - confirming the factory still emits the real FQCN, not the alias.

No behavior change; existing fixtures pass unchanged.