Add api.structured; switch structured kernels to use const Tensor& everywhere (#51490)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/51490
Mutable Tensor ref is a source of endless confusion for kernel writers;
if we're going to make everyone rewrite their kernels, might as well
also get rid of mutable Tensor& while we're at it.
This is a refactor-then-small-update double whammy. The refactor
is to separate tools.codegen.api.structured from api.native for
describing the type signatures of structured kernels (previously,
I was naughtily reusing native for this purpose--now I need it to
behave differently as Tensor). This started off as a copy paste, but
since there are not that many structured kernels so far I could delete
all of the legacy logic from native that didn't make sense (without
having to go out and fix all the use sites all at once).
One more small addition was teaching translate to convert Tensor& to const Tensor&.
Signed-off-by: Edward Z. Yang <ezyang@fb.com>
Test Plan: Imported from OSS
Reviewed By: bhosmer
Differential Revision: D26182413
Pulled By: ezyang
fbshipit-source-id: ed636866add3581179669cf9283f9835fcaddc06
