Add some very basic support for DoLoadImage and UnloadImage for Windows. This was previously not implemented and would result in a failure at runtime that is hard to detect.
This implementation is extremely limited but serves as a starting point for proper support for loading a library. Ideally, the user input would be converted from UTF-8 to UTF-16. This requires additional heap allocations and conversion logic. Error recovery there requires additional allocations both from the local heap and the global heap.
This support enables the use of LLDB's Swift REPL on Windows.