for
Executes a given function on all the neighbours of a given node.
More performant than retrieving a copied list of nodes and calling forEach on them. NOTE: For performance, the node is not validated. Passing a node that isn't in the graph results in undefined behaviour (e.g. Graph will add it as a new node, and Grid may process a different tile's neighbours).
Parameters
node
The node whose neighbours we want to process
action
The function to be called on each neighbour