Reimplement "Drive Mode"

Early versions of WZ had a feature called "Drive Mode".

An example of how it functioned on PSX is viewable in this video: https://youtu.be/Qup6e2MYU-w?feature=shared&t=923

(It let you drive a unit / group and engage enemies. It also automatically swapped focus to the next unit in your squad, when the current took too much damage. And some other interesting functionality that was presumably necessary on a device with only controller input, like the PSX, like camera positioning.)

This was removed due to being broken many years ago (commit for reference: https://github.com/Warzone2100/warzone2100/commit/8f620fc487503a0d157ccf5c4bdddadaf8651de1)

We've had some interest in resurrecting this feature in some capacity, so this issue has been created to collect as much information as possible.

NOTEs:

• It should seemingly be possible to reimplement this in a way that works for all game modes (even if it might not be the most useful in multiplayer) by ensuring that it uses the same pathways to ordering and controlling units as everything else, and essentially functions as a very clever camera mode. (Implementing it with any sort of direct control of units outside of those pathways would likely break multiplayer sync, and skirmish replays, without additional work - like having a new pathway for those drive commands to go through the netqueues?)
• Some of the existing "warcam" functionality may require fixes / calculation adjustments (as the stuff that remains has some edge case issues, currently).