fix IPersist.GetClassID to TYPE_CHECKING only method from Callable annotation

[junkmd]

THIS IS FOR drop_py2 PLAN! Please see #392.

Since Callable cannot tell the IDE the docstring or argument names, it should be changed to use the normal method writing style.

comtypes/comtypes/__init__.py

Lines 853 to 862 in 9238cc7

	class IPersist(IUnknown):
	_iid_ = GUID("{0000010C-0000-0000-C000-000000000046}")
	_idlflags_ = []
	_methods_ = [
	COMMETHOD([], HRESULT, "GetClassID", (["out"], POINTER(GUID), "pClassID")),
	]
	if TYPE_CHECKING:
	# Returns the CLSID that uniquely represents an object class that
	# defines the code that can manipulate the object's data.
	GetClassID: Callable[[], GUID]

A specification of the derived classes of IUnknown is below;
If the names of attributes defined from _methods_ by _cominterface_meta(and _memberspec stuffs) are duplicated in the names of already defined attributes, the names of the methods defined by the metaclasses will be prefixed with _.

comtypes/comtypes/__init__.py

Lines 550 to 552 in 9238cc7

	# We install the method in the class, except when it's a property.
	# And we make sure we don't overwrite a property that's already present.
	mthname = name if not hasattr(self, name) else ("_%s" % name)

comtypes/comtypes/__init__.py

Lines 562 to 563 in 9238cc7

	# Again, we should not overwrite class attributes that are already present.
	propname = name if not hasattr(self, name) else ("_%s" % name)

So the following could be implemented as a "normal" Python method;

class IPersist(IUnknown):
    ...
    def GetClassID(self) -> GUID:
        """Returns the CLSID that uniquely represents an object class that
        defines the code that can manipulate the object's data.
        """
        return self._GetClassID()

But the IPersist.GetClassID is currently untested, and I am not sure that changing it will not result in unexpected regressions.
I will define it once under the if TYPE_CHEKING bridge, knowing that inspect will not work well enough in runtime.

[junkmd]

I created this issue to serve as a "model case" for future good first issue that I will submit.

I will work on this.