[TypeDeclaration] Add NarrowBoolDocblockReturnTypeRector

[TomasVotruba]

Add NarrowBoolDocblockReturnTypeRector: narrows @return docblock bool to false or true when the native return type only allows one of them.

 /**
- * @return bool|string[]
+ * @return false|string[]
  */
 public function run(): false|array

• Native return type must be a union containing exactly one of false/true (not both, not bool).
• Docblock @return must be a union containing bool.
• Swaps the bool node in-place, preserving the rest of the union.
• Docblock-only change, no PHP version bump.