Interop: Merge Interop into Engine library

[capnkenny]

There has been a very floating talk about potentially merging the Interop library into the Engine library. (aka. it was brought up one or two times but I don't remember specifics)

What's pros vs. cons for this?

@FiniteReality @tannergooding @RubyNova

[capnkenny]

FWIW, this is post-MVP.

ATM, I can see that it would condense us to only having one particular library to link against, which may save for some headache on the Interop side. I'm unsure of if this causes issues down the road, however.