[jit] Pull (most) tests out of libtorch_python (#44795)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/44795
Today, we build our cpp tests twice, once as a standalone gtest binary,
and once linked in `libtorch_python` so we can call them from
`test_jit.py`.
This is convenient (it means that `test_jit.py` is a single entry point
for all our tests), but has a few drawbacks:
1. We can't actually use the gtest APIs, since we don't link gtest into
`libtorch_python`. We're stuck with the subset that we want to write
polyfills for, and an awkward registration scheme where you have to
write a test then include it in `tests.h`).
2. More seriously, we register custom operators and classes in these
tests. In a world where we may be linking many `libtorch_python`s, this
has a tendency to cause errors with `libtorch`.
So now, only tests that explicitly require cooperation with Python are
built into `libtorch_python`. The rest are built into
`build/bin/test_jit`.
There are tests which require that we define custom classes and
operators. In these cases, I've built thm into separate `.so`s that we
call `torch.ops.load_library()` on.
Test Plan: Imported from OSS
Reviewed By: SplitInfinity, ZolotukhinM
Differential Revision: D23735520
Pulled By: suo
fbshipit-source-id: d146bf4e7eb908afa6f96b394e4d395d63ad72ff
