Sub-cell co-path-finding with dynamic range

NOTE: continues work from #6208.
Sub-cell aware co-path-finding with dynamic range
    
Continued changes from #6208 to IMove.
 - Removed non-sub-cell constructors from Move
 - Enhanced path-finder
 - Sub-cell aware co-path-finding - tries to use the same path for actors from the same cell.
 - Forward adjacent co-path-finding - tries to use a cached path from a forward adjacent cell.

I actually meant to pass in `self` here and then query `Mobile` in the constructor, which is a standard pattern for activities.