Decompositions can be used to fill in meta support where necessary,
assuming the operations they decompose to support meta key.
This PR adds register_meta kwarg to register_decomposition that
optionally lets you register the meta to the C++ dispatch table
for meta tensors. I use this to then get the meta function for
where and huber_loss for free.
Signed-off-by: Edward Z. Yang <ezyangfb.com>
Pull Request resolved: https://github.com/pytorch/pytorch/pull/77353
Approved by: https://github.com/mruberry
