[aot_autograd] support inplace mutations for subclasses (#120141)
This PR removes the conditional logic depending on requires_subclass_dispatch for mutation handling.
Inputs are labeled with one of three labels: NOT_MUTATED, MUTATED_IN_GRAPH, or MUTATED_OUT_GRAPH. MUTATED_IN_GRAPH indicates mutation that is allowed in the aot autograd graph; MUTATED_OUT_GRAPH indicates mutation that is not allowed in the graph, so the result is computed, returned, and then assigned back to the input after the graph.
Previously, there was logic to handle subclasses differently, so that MUTATED_IN_GRAPH + subclasses would behave like MUTATED_OUT_GRAPH.
This PR simplifies aot_autograd's handling of mutations so that MUTATED_IN_GRAPH will always be handled in graph, even when subclasses are present. Note that there are still some cases where subclass support won't be handled correctly.
Differential Revision: [D53950999](https://our.internmc.facebook.com/intern/diff/D53950999)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/120141
Approved by: https://github.com/bdhirsh
