Add mypy self check benchmark

[JukkaL]

Add benchmark that type checks mypy using mypy.

Try to make this work with earlier mypyc revisions so that we can generate some historical data as well.

[97littleleaf11]

IMO this benchmark is really useful for both mypy and mypyc.

[97littleleaf11]

Suggested by Jukka, these benchmarks would be useful for developing mypyc and mypy:

1. use latest mypyc to compile mypy 0.910 then type-check mypy 0.910 (or some real-world projects of specific verison)
2. use latest mypyc to compile latest mypy then type-check mypy 0.910