[JIT] Fix bug in get_annotation_str for ast.Subscript (#48741)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/48741
**Summary**
This commit fixes a bug in the handling of `ast.Subscript` inside
`get_annotation_str`. `annotation.value` (which contains the AST node
representing the container name) should also be processed using
`get_annotation_str`.
**Test Plan**
This commit adds a unit test to `TestClassType` based on the test case
from the issue that reported this bug.
**Fixes**
This commit fixes #47570.
Test Plan: Imported from OSS
Reviewed By: ppwwyyxx
Differential Revision: D25286013
Pulled By: SplitInfinity
fbshipit-source-id: 61a9e5dc16d9f87b80578f78d537f91332093e52
