Doom style monster movement as an alternate pathfinding mode

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This adds a new mode of monster navigation that is heavily based on how Doom's mobs work. This style of pathfinding does not find the most optimal route to the player, but it does get the player eventually by following walls / ledges and steering in the general direction of the player.

Benefits of this pathfinding style:

• Does not require walking the level to make a node graph, which can be SUPER slow depending on level size
• Handles mobs walking on static entities better
• Handles mobs chasing arbitrary targets
• Handles large groups of mobs better, they will steer around each other instead of getting clumped up
• Never need to walk the node graph, which can be slow enough right now that it happens on another thread

Disadvantages:

• Monsters will not follow the direct path to the player, could make it easier to run away from slower monsters
• CPU hit of pathfinding will now be based on the number of alerted monsters, instead of being a constant hit.

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The default style of mob movement is still the NodeGraphPathfinding, to try out these changes easily check out commit de34f195c05f7f3461e4dbb33fc19defe76e46dc which has this Doom-style pathfinding as the default instead.