fix CoCreateInstance type annotation

[junkmd]

CoCreateInstanceEx is annotated with a return value based on the type variable passed as an argument.

comtypes/comtypes/__init__.py

Lines 1095 to 1099 in 0f3cf2b

	@overload
	def CoCreateInstanceEx(
	clsid, interface=None, clsctx=None, machine=None, pServerInfo=None):
	# type: (GUID, Type[_T_IUnknown], Optional[int], Optional[str], Optional[COSERVERINFO]) -> _T_IUnknown
	pass

However, CoCreateInstance does not.

comtypes/comtypes/__init__.py

Lines 919 to 922 in 0f3cf2b

	@overload
	def CoCreateInstance(clsid, interface, clsctx=None, punkouter=None):
	# type: (GUID, Type[_T_IUnknown], Optional[int], Optional[pUnkOuter]) -> IUnknown
	pass

Please fix as follows.

    @overload
    def CoCreateInstance(clsid, interface, clsctx=None, punkouter=None):
        # type: (GUID, Type[_T_IUnknown], Optional[int], Optional[pUnkOuter]) -> _T_IUnknown
        pass

[junkmd]

The type hinting related enhancements related to #327 are moving toward inline annotations(not comments), and it is planned to develop on a branch that is based on Python3-only support.

I will assign this issue to myself to work on this to prevent a new branch from being created from master with the wrong annotation.

[kdschlosser]

I believe that all COM interfaces have IUnknown as a base class. So if you are type hinting the return value type hint it as IUnknown.

[junkmd]

_T_IUnknown is the IUnknown-bound type variable.

comtypes/comtypes/__init__.py

Line 780 in 0f3cf2b

_T_IUnknown = TypeVar("_T_IUnknown", bound="IUnknown")

And this "serve as the parameters for generic function definitions".

# they are examples of the type analyzer behavior. In runtime, they are not available.
a = CoCreateInstance(GUID(), IUnknown)  # `a` is recognized as `IUnknown` instance by type analyzer.
b = CoCreateInstance(GUID(), IPersist)  # `b` is recognized as `IPersist` instance by type analyzer.
c = CoCreateInstance(GUID(), IServiceProvider)  # `c` is recognized as `IServiceProvider` instance by type analyzer.