This replaces the static functions used for creating
NativeProcessProtocol instances with a factory pattern, and modernizes
the interface of the new class in the process -- I use llvm::Expected
instead of the Status+value combo. I also move some of the common code
(like the Delegate registration into the base class). The new
arrangement has multiple benefits:
- it removes the NativeProcess*** dependency from Process/gdb-remote (which for example means that liblldb no longer pulls in this code).
- it enables unit testing of the GDBRemoteCommunicationServerLLGS class (by providing a mock Native Process).
- serves as another example on how to use the llvm::Expected class (I couldn't get rid of the Initialize-type functions completely here because of the use of shared_from_this, but that's the next thing on my list here)
Tests still pass on Linux and I've made sure NetBSD compiles after this.