Viewporter implementaion (#585)

Implementation of the `wp_viewporter` core protocol and some bugfixes

src/helpers/Vector2D.hpp

@@ -35,6 +35,10 @@ class Vector2D {
         return a.x != x || a.y != y;
     }
 
+    Vector2D operator*(const Vector2D& a) const {
+        return Vector2D(this->x * a.x, this->y * a.y);
+    }
+
     Vector2D clamp(const Vector2D& min, const Vector2D& max = Vector2D());
 
     Vector2D floor();