[JIT] Exclude staticmethods from TS class compilation (#42611)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/42611
**Summary**
This commit modifies the Python frontend to ignore static functions on
Torchscript classes when compiling them. They are currently included
along with methods, which causes the first argument of the
staticfunction to be unconditionally inferred to be of the type of the
class it belongs to (regardless of how it is annotated or whether it is
annotated at all). This can lead to compilation errors depending on
how that argument is used in the body of the function.
Static functions are instead imported and scripted as if they were
standalone functions.
**Test Plan**
This commit augments the unit test for static methods in `test_class_types.py`
to test that static functions can call each other and the class
constructor.
**Fixes**
This commit fixes #39308.
Test Plan: Imported from OSS
Reviewed By: ZolotukhinM
Differential Revision: D22958163
Pulled By: SplitInfinity
fbshipit-source-id: 45c3c372792299e6e5288e1dbb727291e977a2af
