Cannot determine type of a function with a no_type_check decorator

[JukkaL]

Mypy complains if I call a no_type_check function above the definition:

import typing

def f() -> None:
    foo()  # Error: Cannot determine type of 'foo'

@typing.no_type_check
def foo(x: {1:2}) -> [1]:
    1 + 'x'

We should detect no_type_check during semantic analysis and set the type of the Decorator object to Any there, before type checking.