[nnc] Use a descriptive name for fused kernels when profiling (#66990)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/66990
NNC fusion groups currently show up as "TensorExpr" in the profiler,
which is true but not super useful since it obscures what's actually happening
in the fusion group. This change will log them as `fused_XXX` where XXX is a
(length-limited) series of ops describing the subgraph, for instance
`fused_mul_add` to represent a group containing `aten::mul`, `aten::add`.
Test Plan: New unit test to check the output of autograd profiler.
Reviewed By: dzhulgakov
Differential Revision: D31762087
fbshipit-source-id: 3fadbdc67b054faa01aa42e5b6ea2c4a6bc3481f
