[JIT] Enable ModuleDict non-literal indexing (#45716)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/45716
**Summary**
This commit enables indexing into `ModuleDict` using a non-literal
index if the `ModuleDict` is annotated with `Dict[str, X]`, where `X` is
a module interface type. These annotations must be expressed using a
class attribute named `__annotations__`, which is a `Dict[str, Type]`
where the keys are the names of module attributes and the values are
their types.
The approach taken by this commit is that these annotations are stored
as "hints" along with the corresponding module attributes in the
`ConcreteSubmoduleTypeBuilder` instance for each module (which might be
a `ModuleDict`). These hints are passed into the `ModuleValue` that is
created for desugaring operations on submodules so that indexing into a
`ModuleDict` can be emitted as a getitem op into a dict emitted into the
graph that represents the `ModuleDict`.
**Test Plan**
This commit adds unit tests to `TestModuleContainers` to test this
feature (`test_typed_module_dict`).
Differential Revision: D24070606
Test Plan: Imported from OSS
Reviewed By: ansley
Pulled By: SplitInfinity
fbshipit-source-id: 6019a7242d53d68fbfc1aa5a49df6cfc0507b992
