Support emitting a CMake module file to enable easy consumption of DNNE-generated headers and libs from native code

[jkoritzinsky]

DNNE is designed to emit both a native binary as well as the headers for consuming said binary. However, DNNE doesn't provide any CMake integration (such as through a file that could be included to define imported targets). As a result, CMake consumers of DNNE APIs need to manually set up imported targets with the correct include paths and linker paths. I've done so in AaronRobinsonMSFT/DNMD#50. It would be nice if DNNE could generate a CMake file that defines an imported target for the build output (and possibly do so for NativeAOT scenarios as well since the exports should have the same shape for a library that uses both DNNE and NativeAOT).