Add function documentation to private functions

Bug: T330644
Depends-On: I2914498869ee8dbee20ca8196ac70b7b70e83b44
Depends-On: I69fb434d5840af45977d0fbc8026faab274e3866
Depends-On: I9db4e5fa87a6d84300c5f9f4e3eddf497ec31739
Change-Id: I1c42b94b1b6683b78b2b4d326bdbecc3353935d3

Author: umherirrender

src/Entity/ItemId.php

@@ -26,6 +26,9 @@ public function __construct( $idSerialization ) {
 		parent::__construct( strtoupper( $idSerialization ) );
 	}
 
+	/**
+	 * @param string $idSerialization
+	 */
 	private function assertValidIdFormat( $idSerialization ) {
 		if ( !is_string( $idSerialization ) ) {
 			throw new InvalidArgumentException( '$idSerialization must be a string' );

src/Entity/NumericPropertyId.php

@@ -22,6 +22,9 @@ public function __construct( $idSerialization ) {
 		parent::__construct( strtoupper( $idSerialization ) );
 	}
 
+	/**
+	 * @param string $idSerialization
+	 */
 	private function assertValidIdFormat( $idSerialization ) {
 		if ( !is_string( $idSerialization ) ) {
 			throw new InvalidArgumentException( '$idSerialization must be a string' );

src/Entity/SerializableEntityId.php

@@ -25,6 +25,9 @@ public function __construct( $serialization ) {
 		$this->serialization = self::normalizeIdSerialization( $serialization );
 	}
 
+	/**
+	 * @param string $serialization
+	 */
 	private static function assertValidSerialization( $serialization ) {
 		if ( !is_string( $serialization ) ) {
 			throw new InvalidArgumentException( '$serialization must be a string' );

src/Statement/StatementByGuidMap.php

@@ -64,6 +64,9 @@ public function hasStatementWithGuid( $statementGuid ) {
 		return array_key_exists( $statementGuid, $this->statements );
 	}
 
+	/**
+	 * @param string $statementGuid
+	 */
 	private function assertIsStatementGuid( $statementGuid ) {
 		if ( !is_string( $statementGuid ) ) {
 			throw new InvalidArgumentException( '$statementGuid needs to be a string' );