[processor] Add 'model input names' property (#20117)

* [processor] Add 'model input names' property

* add test

* no f string

* add generic property method to mixin

* copy to multimodal

* copy to vision

* tests for all audio

* remove ad-hoc tests

* style

* fix flava test

* fix test

* fix processor code

tests/models/wav2vec2/test_processor_wav2vec2.py

@@ -137,3 +137,15 @@ class Wav2Vec2ProcessorTest(unittest.TestCase):
         decoded_tok = tokenizer.batch_decode(predicted_ids)
 
         self.assertListEqual(decoded_tok, decoded_processor)
+
+    def test_model_input_names(self):
+        feature_extractor = self.get_feature_extractor()
+        tokenizer = self.get_tokenizer()
+
+        processor = Wav2Vec2Processor(tokenizer=tokenizer, feature_extractor=feature_extractor)
+
+        self.assertListEqual(
+            processor.model_input_names,
+            feature_extractor.model_input_names,
+            msg="`processor` and `feature_extractor` model input names do not match",
+        )