[Misc] Replace is_encoder_decoder_inputs with split_enc_dec_inputs (#15620)

Signed-off-by: DarkLight1337 <tlleungac@connect.ust.hk>

tests/models/multimodal/processing/test_idefics3.py

@@ -29,7 +29,7 @@ def test_processor_override(
     num_imgs: int,
     kwargs_on_init: bool,
 ):
-    """Ensure input_processor_for_idefics3 handles num_crops properly."""
+    """Ensure Idefics3MultiModalProcessor handles num_crops properly."""
     # Same as the previous test - don't initialize mm_processor_kwargs
     # in this test and assume that the kwargs will be correctly expanded by
     # the partial when calling the custom input processor.