A "what can my opponents see about me?" view

**What do you want to see?**
I want to add a special view mode in the GUI that lets you choose an opponent and then display only what you know that they can see. So if they have a ship in some system, then they can see your colonies and uncloaked ships there; if you happen to know that that ship has tachyon sensors, then they can see your cloaked ships too. This would of course also apply to other empires' ships/colonies/etc as well, be they allies or enemies or whatever.

The button to activate this mode could go on the empires list screen (near each empire) or the empire status screen for each empire. To deactivate it, you would just activate it for yourself, or maybe closing the main game window would bring you back to your own view. Perhaps it could even be nested, if you open empire A's view then empire B's view without returning to your own first, it would actually let you see what you know that empire B knows that empire A knows? But would that even be useful?

We could call it "opponent view" or maybe "impersonation view". "Counter-intel view" sounds cool but counter-intel already means something particular in SE4...

**How would it help players?**
It would give them a better strategic overview of the map and what their opponents know about them. Maybe even about more than the map - empire reports etc?

**Alternatives**
N/A

**Screenshots and mockups**
N/A

**Things to consider**
In theory, this would be as simple as calling the `Redact` function on the already redacted game state; this was one of the first ideas I had for FrEee when I created the project! However it might get tricky when trying to swap game states on the fly in the GUI. If that's not possible, we might need to reload the GUI from scratch. Maybe if I can get savegame sizes down, I could even include all these double redacted game states in each player's game state somehow (as a referenced object or a zip file?) so they don't need to be generated on the fly when the player needs them, which could be time consuming?

It might be useful to also show things that your opponent *can't* see but you can (e.g. your cloaked ships) but in some special fashion (similar to fogged objects?), just for reference. But that would take some thought as the Redact function would need to be modified to do only a partial redaction in this scenario, leaving memories (or something like that) of fogged objects... but then those "memories" shouldn't be taken into account when computing empire statistics and system abilities, so they would need some sort of special flag on them to disable those features...