bpo-38163: Child mocks detect their type as sync or async

[lisroach]

This should be the last diff to get the child mocks detecting their type as either synchronous or asynchronous and returning AsyncMock or MagicMock (or Mock) depending on their type.

The main goal is for classes that have a mix of asynchronous and synchronous methods to auto-detect whether they should be AsyncMock or a synchronous mocks. Example:

  >>> class ExampleClass:
  ...     def sync_foo():
  ...         pass
  ...     async def async_foo():
  ...         pass
  ...
  >>> a_mock = AsyncMock(ExampleClass)
  >>> a_mock.sync_foo
  <MagicMock name='a_mock.sync_foo' id='...'>
  >>> a_mock.async_foo
  <AsyncMock name='a_mock.async_foo' id='...'>
  >>> mock = Mock(ExampleClass)
  >>> mock.sync_foo
  <Mock name='mock.sync_foo' id='...'>
  >>> mock.async_foo
  <AsyncMock name='mock.async_foo' id='...'>

This defies Mock's typical functionality where all child mocks follow the type of their parent mock, but after some discussion I believe the auto-detection is more important to the typical user than a consistency with current Mock style.

https://bugs.python.org/issue38163

[miss-islington]

Thanks @lisroach for the PR 🌮🎉.. I'm working now to backport this PR to: 3.8.
🐍🍒⛏🤖

[miss-islington]

I'm having trouble backporting to 3.8. Reason: 'Error 110 while writing to socket. Connection timed out.'. Please retry by removing and re-adding the needs backport to 3.8 label.

[miss-islington]

Thanks @lisroach for the PR 🌮🎉.. I'm working now to backport this PR to: 3.8.
🐍🍒⛏🤖

[miss-islington]

Sorry @lisroach, I had trouble checking out the 3.8 backport branch.
Please backport using cherry_picker on command line.
cherry_picker 3667e1ee6c90e6d3b6a745cd590ece87118f81ad 3.8

[bedevere-bot]

GH-16484 is a backport of this pull request to the 3.8 branch.