Fixed vehicles can't move to nearby walled tile

The fix for #6989 is mainly done in lines 73,74 in OpenRA.Mods.RA/Move/PathFinder.cs, rest of the patch is mainly naming convention changes. I'm aware that they might be wrong since this is my first pull request to this project.

Anyway the reason for this bug is that the first fromSrc.Expand-call doesn't add the grid position where the vehicle is located to the queue as there is no self awareness in the directional search that's moving towards the vehicle, this makes the search end early since that queue will be empty.