arePositionsEqualOrAdjacent = function (positionA, positionB) {
  return Math.abs(positionA.x - positionB.x) <= 1 && Math.abs(positionA.y - positionB.y) <= 1;
}
Returns whether two positions are equal or adjacent.
@param {Vec2} positionA
@param {Vec2} positionB
@returns {Boolean}