Improve random spawn (#2503)

## Description:

This is a previously approved PR with an additional commit that fixes
case when nations change spawn & jump around, their previous territory
wasn't getting deleted.

## Please complete the following:

- [x] I have added screenshots for all UI updates
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [x] I have added relevant tests to the test directory
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced

## Please put your Discord username so you can be contacted if a bug or
regression is found:

nikolaj_mykola

---------

Co-authored-by: Evan <evanpelle@gmail.com>

src/core/game/Game.ts

@@ -550,7 +550,8 @@ export interface Player {
   markDisconnected(isDisconnected: boolean): void;
 
   hasSpawned(): boolean;
-  setHasSpawned(hasSpawned: boolean): void;
+  setSpawnTile(spawnTile: TileRef): void;
+  spawnTile(): TileRef | undefined;
 
   // Territory
   tiles(): ReadonlySet<TileRef>;