[jit] jit._drop fun modifier to allow in jit class non-jit decl funs (#93012)
`@torch.jit.unused` and `@torch.jit.ignore` do not allow to keep in torch scripted class member function, that has non scriptable declaration (e.g. return type)
Adding FunctionModifier _DROP to allow fully skip those functions from scripting and keep them in the code of the scripted class.
E.g. it can be used for:
```
@torch.jit._drop
def __fx_create_arg__(self, tracer: torch.fx.Tracer) -> torch.fx.node.Argument:
# torch.fx classes are not scriptable
return tracer.create_node(
"call_function",
CFX,
args=(tracer.create_arg(self.features),),
kwargs={},
)
def __iter__(self) -> Iterator[torch.Tensor]:
return iter(self.a)
```
Testing:
Added test case in `test/jit/test_types.py` with non-scriptable type annotations (fx.* classes) that fails before fix and passes after.
```
python test/test_jit.py
```
Differential Revision: [D42774830](https://our.internmc.facebook.com/intern/diff/D42774830)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/93012
Approved by: https://github.com/davidberard98
