Determine data for thru points for movement times

[Zannick]

This would allow us to simplify graphs around water surfaces, for example, since we could just set thru points inside the map area that would pick up the datamap attributes, rather than entire new spots.

[Zannick]

If we were able to determine what area a thru point belongs to, potentially we could use that for accurate simulation of moving through multiple areas (especially for AV2's on_entry rules).