return md5 hash of executable file in the `qModuleInfo` response when no build ID is available

The response to `qModuleInfo` contains the executable file's embedded build ID as a "uuid" field. For executable files that don't have a build ID, calculate an md5 hash of the file, contents and return that as an "md5" field instead of the "uuid" field.

https://github.com/compnerd/ds2/blob/6c269217da706efc3db9c6e04245c62dc4d35ac8/Sources/GDBRemote/Mixins/FileOperationsMixin.hpp#L104-L115

Also consider implementing support for `vFile:MD5` in `Session::Handle_vFile` since it could reuse the same implementation.