Add 'Literal[...]' to typing_extension stubs (#2664)
Add 'Literal[...]' to typing_extension stubs (#2664)

This pull request adds 'Literal' to the typing_extension stubs
and serves as the dual of this PR:
https://github.com/python/typing/pull/591

For background context, here's the associated PEP draft:
https://github.com/Michael0x2a/peps/pull/1
euresti/typeshed