Add immutable dict support (#16208)
Summary:
This PR adds basic support (creation and indexing) for immutable dictionaries in Script. This includes Python/string frontend support and a `IValue::GenericDict` type backed by a `std::unordered_map`. Only `str`, `int`, and `float` are supported as keys, any type can be a value. Structure is pretty similar to list.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/16208
Differential Revision: D13881686
Pulled By: driazati
fbshipit-source-id: 29ce9835b953c3456f57bcc2bbdf7fe0cbf941c0
