Centralize addition of "always on" dispatch keys. (#32734)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/32734
VariableTensorId is the only key with this treatment today,
but BackendSelect and CompoundOp are coming soon.
Signed-off-by: Edward Z. Yang <ezyang@fb.com>
Test Plan: Imported from OSS
Differential Revision: D19628091
Pulled By: ezyang
fbshipit-source-id: 250753f90528fa282af7a18d8d2f7736382754bd
