Activator performance improvement

Shouldn't close the previous PR early. Turns out I did not have to change much of my design.

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@pranavkm
@halter73 
@rynowak
@ipjohnson
@yishaigalatzer 
If this code path gets hit, and the ITypeActivator implementation depends on another service that requires the ITypeActivator to be resolved, a StackOverflowException will result. We should really get rid of this class.