Video core: Add utility class for vector operations.

I wrote most of this for ppsspp, so I hold full copyright over it.
In addition to the original release in ppsspp, this provides functionality to easily extend e.g. two-dimensional vectors to three-dimensional vectors.

src/video_core/video_core.vcxproj

@@ -25,6 +25,7 @@
   </ItemGroup>
   <ItemGroup>
     <ClInclude Include="gpu_debugger.h" />
+    <ClInclude Include="math.h" />
     <ClInclude Include="pica.h" />
     <ClInclude Include="renderer_base.h" />
     <ClInclude Include="utils.h" />