Common: Add a Result class

This adds a lightweight, easy to use std::variant wrapper intended to
be used as a return type for functions that can return either a result
or an error code.

Source/Core/Common/Common.vcxproj

@@ -138,6 +138,7 @@
     <ClInclude Include="PcapFile.h" />
     <ClInclude Include="Profiler.h" />
     <ClInclude Include="QoSSession.h" />
+    <ClInclude Include="Result.h" />
     <ClInclude Include="ScopeGuard.h" />
     <ClInclude Include="SDCardUtil.h" />
     <ClInclude Include="Semaphore.h" />