The testing framework dlls come from mono and their paths are harcoded
in the templates. Move the hardcoded paths out to the assembly locator
which know were to find the paths.
This is needed to later allow the cmd to pass the location of the paths.
The Generator and the Factory classes are a xamarin-macios thing.
Initially, they were separated because the code that generated the bcl
tests was not inside xharness. That is not longer the case. We can merge
both classes, generalize the namespace and be more prepared to move out
of the xamarin-macios repo.