Call _set_save_spec() when creating TF models (#19321)
* Add a build_from_serving_sig_and_dummies method and replace all calls like model(model.dummy_inputs) with it.
* make fixup
* Remove the overridden save() as this is no longer necessary
* Also call _set_save_spec(), the last missing piece
* Ensure we set the save spec when loading from config too
* Turn this whole thing into a one-line PR
* Turn this whole thing into a one-line PR
* Turn this whole thing into a one-line PR
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