Re-enable Phan and fix warnings for `data-model-serialization'

Some directories are excluded from Phan checks as a result of
T289040. .phan/config.php includes the folders for the
libraries in exclude_analysis_directory_list. Enabling Phan
checks results in a build failure.

Resolve the Phan warnings and re-enable checks for the
`data-model-serialization/src` folder.

Bug: T353623
Change-Id: Iba7ecbbc8c76055bb4a40f1cf9ca8f7126649754

Author: codders

src/Deserializers/SnakDeserializer.php

@@ -159,7 +159,7 @@ private function needsDataTypeLookup( string $valueType ): bool {
 			array_keys( $this->dataTypeToValueTypeMap, $valueType, true )
 		);
 
-		return !empty( array_intersect( $possibleDataTypeKeys, array_keys( $this->deserializerBuilders ) ) );
+		return array_intersect( $possibleDataTypeKeys, array_keys( $this->deserializerBuilders ) ) !== [];
 	}
 
 	/**

src/Serializers/AliasGroupListSerializer.php

@@ -26,7 +26,7 @@ public function __construct( AliasGroupSerializer $aliasGroupSerializer, bool $u
 
 	/**
 	 * @param AliasGroupList $object
-	 * @return array|::stdClass
+	 * @return array|\stdClass
 	 */
 	public function serialize( $object ) {
 		$this->assertIsSerializerFor( $object );

src/Serializers/MapSerializer.php

@@ -31,7 +31,7 @@ public function __construct( bool $useObjectsForEmptyMaps ) {
 	 * @return array|\stdClass
 	 */
 	protected function serializeMap( array $serialization ) {
-		if ( $this->useObjectsForEmptyMaps && empty( $serialization ) ) {
+		if ( $this->useObjectsForEmptyMaps && $serialization === [] ) {
 			$serialization = (object)$serialization;
 		}