Add overlays to clear before current draw/pass. Refs #164

* Depth is not cleared, only colour buffers.
* This uses the same definition of pass as the quad overdraw overlay,
  which isn't quite the same as the auto-grouping passes (which allow
  for varying colour binds being grouped together). It only counts up
  to the last draw where the outputs were different.

renderdoc/api/replay/replay_enums.h

@@ -128,12 +128,14 @@ enum TextureDisplayOverlay
 	eTexOverlay_None = 0,
 	eTexOverlay_Drawcall,
 	eTexOverlay_Wireframe,
-	eTexOverlay_DepthBoth,
-	eTexOverlay_StencilBoth,
+	eTexOverlay_Depth,
+	eTexOverlay_Stencil,
 	eTexOverlay_BackfaceCull,
 	eTexOverlay_ViewportScissor,
 	eTexOverlay_NaN,
 	eTexOverlay_Clipping,
+	eTexOverlay_ClearBeforePass,
+	eTexOverlay_ClearBeforeDraw,
 	eTexOverlay_QuadOverdrawPass,
 	eTexOverlay_QuadOverdrawDraw,
 };