Expose hooks to process input args in precision plugins

[awaelchli]

Proposed refactor

Motivation

#12983 attempted to fix an issue where the evaluation step methods in the DDPStrategy would call the LightningModule.x_step methods directly instead of going through the LightningDoublePrecisionModule.x_step methods.

This introduced a typing issue where we can't guarantee that self.model implements the x_step methods.

Pitch

Treat #12983 as a temporary fix and refactor away the need to have a precision wrapper.
All the precision wrapper does is process the input arguments.
This input processing could be done directly in the strategy.

Before

    def test_step(self, *args, **kwargs) -> Optional[STEP_OUTPUT]:
        with self.precision_plugin.test_step_context():
            return self.MAYBE_WRAPPER.test_step(*args, **kwargs)

After

    def test_step(self, *args, **kwargs) -> Optional[STEP_OUTPUT]:
        with self.precision_plugin.test_step_context():
            return self.LIGHTNING_MODULE.test_step(self.precision_plugin.process_step_inputs(*args, **kwargs))

Additional context

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cc @justusschock @awaelchli @rohitgr7 @carmocca @akihironitta

[carmocca]

Sounds good to me. A relevant PR that still needs to land: #10079