I don't need pathfinding because I am not trying to create an isometric RPG where the player runs to the place you clicked, which is much more complicated, I believe.
I want the player only to be able to move towards the mouse cursor only when he is holding down the mouse button, as seen in the example.
I was assuming it only requires some slight modifications to my example as it seems to be working the way I want, except the smooth wall-collision part.
To give you a better understanding, I want the walls to have the same effect as "Bound to Layout" does. Try walking out of the layout - you can see the player still moves towards the mouse but the character doesn't stop moving.