Adds CallActivityFunc & IMove.MoveIntoTarget and Fixes #4640 - Units teleport into transports

CallActivityFunc is actually used by Mobile.MoveIntoTarget to provide Mobile.VisualMove with the current position of the target.
IMove.MoveIntoTarget is used by the fix and will be used by future Exit/Dock logic.

Fixes #4640 - Units teleport into transports.
Style nit: this looks like it should be readonly.