Issue 38163: AsyncMock child mocks should detect their type

We want child mocks to match their "type" (async or sync). 

Ex:

class Prod:
   async def foo():
      pass
    def bar():
       pass

a_mock = AsyncMock(Prod)
isinstance(a_mock.foo(), AsyncMock) == True
isinstance(a_mock.bar(), MagicMock) == True

Also this should include magic methods:

int(a_mock) should work and return 1 like MagicMocks do.
a_mock.__enter__ should exist and be a MagicMock, just as a_mock.__aenter__ exists and is an AsyncMock.

This should be simple to do, after https://github.com/python/cpython/pull/16060 we can add:

            elif self._mock_methods and _new_name in self._mock_methods:
                # Methods that are not in _spec_asyncs are normal methods
                klass = MagicMock

to _get_child_mocks and test with:

    def test_normal_methods_on_class(self):
        am = AsyncMock(AsyncClass)
        self.assertIsInstance(am.async_method, AsyncMock)
        self.assertIsInstance(am.normal_method, MagicMock)

This might be starting to make _get_child_mocks too complicated, and no longer follows the default "child mocks are the same as their parent". I am not sure how to redefine _get_child_mocks without needing to double up a lot of code to support MagicMocks having AsyncMock child_mocks as well.

Lately I have been having my doubts around having MagicMocks also create AsyncMocks as children. 

Should a MagicMock really have a __aenter__ magic method? 
Is this too far from the original MagicMock if we change child mocks to default not to their parent type, but to their parent type *or* AsyncMock if asynchronous?

It makes the using the mocks easier, since you can just use MagicMock or AsyncMock for whatever you are doing and not think about when to use which. But it also might make the code more confusing, since it isn't as clear when to use one or the other.

New changeset 3667e1ee6c90e6d3b6a745cd590ece87118f81ad by Lisa Roach in branch 'master':
bpo-38163: Child mocks detect their type as sync or async (GH-16471)
https://github.com/python/cpython/commit/3667e1ee6c90e6d3b6a745cd590ece87118f81ad

New changeset 21f24ead90c22d0e2c2ebf14a64b37d99de54b33 by Lisa Roach in branch '3.8':
[3.8] bpo-38163: Child mocks detect their type as sync or async (GH-16471) (GH-16484)
https://github.com/python/cpython/commit/21f24ead90c22d0e2c2ebf14a64b37d99de54b33