@overload declarations in stubs - required to be directly adjacent?

Bug Report

Currently, mypy requires @overload declarations in stubs to be directly adjacent, with no declarations (e.g. type vars) in between. However, I don't find that requirement in PEP 484 [1], nor in the typing module documentation [2].

[1] https://www.python.org/dev/peps/pep-0484/#function-method-overloading
[2] https://docs.python.org/3/library/typing.html#typing.overload

To Reproduce
Consider the following type stub:

import typing

@typing.overload
def foo() -> None: ...

K = typing.TypeVar('K')
@typing.overload
def foo(k: K) -> K: ...

Then run stubtest on it.

Expected Behavior
According to the documentation, I would expect this stub to be valid.

Actual Behavior

$ python -m mypy.stubtest teststub
error: failed mypy build.
teststub.pyi:4: error: Single overload definition, multiple required
teststub.pyi:8: error: Name 'foo' already defined on line 4
teststub.pyi:8: error: Single overload definition, multiple required

Pulling the type var declaration up fixes it:

import typing

K = typing.TypeVar('K')

@typing.overload
def foo() -> None: ...

@typing.overload
def foo(k: K) -> K: ...

Your Environment
Python 3.7.1 (anaconda) on Linux, latest master of mypy.
I also tested with mypy 0.790 on Windows, with the same result.

$ python --version
Python 3.7.1
$ python -m mypy --version
mypy 0.820+dev.497556f466dcda90d850b23e86c55ec4082be3f5

Start by reproducing the failure with the shown teststub and python -m mypy.stubtest teststub. Trace how mypy validates adjacent @typing.overload declarations and add a regression test covering the intervening TypeVar; done means the stub is accepted while existing overload diagnostics remain correct.