[FX] Add type annotation to `getitem` node before `split_module` (#88510)
Summary: Some nodes lost the type annotation during `split_module`, causing the submodels to be un-scriptable. This is because compiler always infer Tensor type, which is wrong for non-Tensor types. We attempt to infer type annotation for `getitem` node to improve scriptability.
Test Plan:
```
buck2 test //caffe2/test:fx_experimental
```
Differential Revision: D41037819
Pull Request resolved: https://github.com/pytorch/pytorch/pull/88510
Approved by: https://github.com/xush6528
