Add "Movement distance modifier" Scene Region behavior

[KitCat420]

As per title, adding a new Scene Region Behavior that allows modifying how much distance is consumed when this scene region is being crossed would allow modelling different use cases, most importantly difficult terrain for many systems.

On the example of difficult terrain: The user would set up a scene region, stat it with a "Movement distance modifier" behavior of 2, then Drag Ruler can utilize that information when measuring through said region to adjust the total distance measured accordingly.

This functionality would essentially superseed things like the Terrain Ruler/TerrainLayer integration.