Move TF building to an actual build() method (#23760)

* A fun new PR where I break the entire codebase again

* A fun new PR where I break the entire codebase again

* Handle cross-attention

* Move calls to model(model.dummy_inputs) to the new build() method

* Seeing what fails with the build context thing

* make fix-copies

* Let's see what fails with new build methods

* Fix the pytorch crossload build calls

* Fix the overridden build methods in vision_text_dual_encoder

* Make sure all our build methods set self.built or call super().build(), which also sets it

* make fix-copies

* Remove finished TODO

* Tentatively remove unneeded (?) line

* Transpose b in deberta correctly and remove unused threading local

* Get rid of build_with_dummies and all it stands for

* Rollback some changes to TF-PT crossloading

* Correctly call super().build()

tests/models/vision_encoder_decoder/test_modeling_tf_vision_encoder_decoder.py

@@ -729,9 +729,9 @@ class TFVisionEncoderDecoderModelSaveLoadTests(unittest.TestCase):
 
         # create two random ViT/GPT2 models for vit-gpt2 & initialize weights (+cross_attention weights)
         encoder = TFViTModel(config.encoder)
-        encoder(encoder.dummy_inputs)
+        encoder.build()
         decoder = TFGPT2LMHeadModel(config.decoder)
-        decoder(decoder.dummy_inputs)
+        decoder.build()
 
         encoder_decoder_orig = TFVisionEncoderDecoderModel(encoder=encoder, decoder=decoder)