[UPDATED PROTOTYPE] Use dynamo fake tensor mode in aot_autograd, move aot_autograd compilation to lowering time
After all of the preparatory commits, this is a subset of the
changes in https://github.com/pytorch/pytorch/pull/89392 that actually
change us to propagating fake tensors to backends.
Signed-off-by: Edward Z. Yang <ezyangfb.com>
ghstack-source-id: 8684d1d66d559cd1b40bdca6370aa2f6fb513bda
Pull Request resolved: https://github.com/pytorch/pytorch/pull/89672
