Activator performance improvement

Shouldn't close the previous PR early. Turns out I did not have to change much of my design.

Pinging previous trackers
@pranavkm
@halter73 
@rynowak
@ipjohnson
@yishaigalatzer 
Are we going to expect every container to have an ITypeActivator registered by default like we do for IServiceProvider and IServiceScopeFactory? If so, we would need to change our Populate methods for Autofac and Ninject.

I really don't like adding a specific service in this part of the code.