Make RegisterKeyedFactory public

[jeeyo]

We exposed AutoWireAssembly<T>() for constructing keysForType dictionary for keyed DI,
but didn't expose RegisterKeyedFactory() to actually register them.

[mbhuiyan730]

How this will be used? can you please provide an example?

[jeeyo]

I wanted to do AutoWireAssembly<T> with my own custom Attribute instead of RegisterSingleton or other built-in attributes like in this method.
But the method RegisterKeyedFactory() was marked as private, so I cannot do so.