Class Factor Source Generator

[shmuelie]

Is your feature request related to a problem? Please describe.
When a COM interface is implemented, a class factory with GeneratedComClass is needed and manually created.

Describe the solution you'd like
A source generator that creates a basic implementation of IClassFactory

Describe alternatives you've considered
Hand coding it

Implementation Ideas

1. A GeneratedClassFactory attribute on the implementing class that results in a generated class factory.

[GeneratedComClass]
[GeneratedClassFactory]
class Foo : IFoo {}

// Generates:
class FooFactory : IClassFactory { /*..*/ }