Vendored types for the stdlib

This crate vendors typeshed's stubs for the standard library. The vendored stubs can be found in crates/ty_vendored/vendor/typeshed. The file crates/ty_vendored/vendor/typeshed/source_commit.txt tells you the typeshed commit that our vendored stdlib stubs currently correspond to.

The typeshed stubs are updated every two weeks via an automated PR using the sync_typeshed.yaml workflow in the .github/workflows directory. This workflow can also be triggered at any time via workflow dispatch.