[JIT] Properly convert Python strings implictly to device (#51340)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/51340
**Summary**
`toIValue` assumes that any value passed for an argument of type
`torch.device` is a valid device object, even when it is not. This can
lead to device type arguments of functions being assigned incorrect
values (see #51098).
This commit adds an explicit check that the passed in object is indeed a
`torch.device` using `THPDevice_Check` and only then does is it
converted to an `IValue`. Since implicit conversion from strings to
devices is generally allowed, if `THPDevice_Check` fails, it is assumed
that the object is a string and an `IValue` containing a `c10::Device`
containing the passed in string is returned.
**Test Plan**
This commit adds a unit test to `test_jit.py` to test that invalid
strings passed as devices are not longer silently accepted.
**Fixes**
This commit fixes #51098.
Test Plan: Imported from OSS
Reviewed By: pbelevich
Differential Revision: D26187190
Pulled By: SplitInfinity
fbshipit-source-id: 48c990203431da30f9f09381cbec8218d763325b
