GPU: Add wireframe rendering/overlay

src/core/gpu_hw_shadergen.h

@@ -18,6 +18,8 @@ public:
                                           bool dithering, bool interlacing);
   std::string GenerateDisplayFragmentShader(bool depth_24bit, GPU_HW::InterlacedRenderMode interlace_mode,
                                             bool smooth_chroma);
+  std::string GenerateWireframeGeometryShader();
+  std::string GenerateWireframeFragmentShader();
   std::string GenerateVRAMReadFragmentShader();
   std::string GenerateVRAMWriteFragmentShader(bool use_ssbo);
   std::string GenerateVRAMCopyFragmentShader();