gpu: draw full screen widgets on gpu

This adjusts the draw callbacks api to take in the color of the full
screen overlay the client would have rendered. This is primarily used in
godwars, underwater, darkmeyer, etc. Having them rasterized on the cpu
is slow, especially with gpu on since we additionally have to compute
the alpha per-pixel.

runelite-api/src/main/java/net/runelite/api/hooks/DrawCallbacks.java

@@ -43,7 +43,12 @@ public interface DrawCallbacks
 						SceneTileModel model, int tileZ, int tileX, int tileY,
 						int zoom, int centerX, int centerY);
 
-	void draw();
+	/**
+	 * Called when a frame should be drawn.
+	 *
+	 * @param overlayColor Color of full-viewport overlays, if any
+	 */
+	void draw(int overlayColor);
 
 	boolean drawFace(Model model, int face);