New lightmapper

-Added LocalVector (needed it)
-Added stb_rect_pack (It's pretty cool, we could probably use it for other stuff too)
-Fixes and changes all around the place
-Added library for 128 bits fixed point (required for Delaunay3D)

core/image.cpp

@@ -3668,6 +3668,10 @@ Ref<Resource> Image::duplicate(bool p_subresources) const {
 	return copy;
 }
 
+void Image::set_as_black() {
+	zeromem(data.ptrw(), data.size());
+}
+
 Image::Image() {
 
 	width = 0;