Details (world preview) screen causes environment/context corruption

[Cervator]

The "Details" button (which lists world config options and allows previewing the world) is at present somewhat problematic. It involves module environment / context switches to be able to activate additional modules (to be able to preview a world gen in a module) which isn't quite solid yet. Some problems:

• The screen stalls the game for a moment as (I believe) it is scanning/enabling the selected modules to be able to present any configurable toggles (it doesn't actually create a world preview, but at this point it might as well)
• On closing the screen it takes a moment again as I guess it reloads the standard environment (without extra modules). But something goes awry here - clicking Details again causes an error and while it doesn't crash the game the client becomes unreliable
• After closing the screen but not re-entering Details the next attempted module/context swap fails, such as exiting away from the create game screen then trying again (modules/world generators fail to list). This seems to break the game client a little worse and you have to process kill the game somehow (different error)
• Not all world types work - for instance Throughout The Ages processes for a while but then fails with the same error as retrying details

The preview / config step does function in some cases and if you immediately start the game it does function. But it seems attempting to tweak further breaks the game. There are some more notes in #1780

An earlier attempt to streamline this was #2068 which was implemented in still-pending PR #2074 by @msteiger. That led to errors some of which at least seem to match the ones even without the PR. Probably there are things we can fix that'll help both cases.

In the meanwhile this is poor usability and even if we can't get back to work on the full #2074 implementation (module / environment context stuff is pretty deep architecture) maybe we can improve the experience.

Worth noting is that when you use the functionality and start a game, then return to the main menu then the environment setup appears to be solid and usable again. Something in the context switch for entering a full game then leaving correctly achieves something that the Details functionality does not.

• The idea in the PR is to actually make configuration / preview a next screen after initial world creation setup, which is behind a progress screen in the PR. Maybe that could be added up front to avoid the appearance of the game stalling
• Whatever error leads to a corrupt environment might be something we can fix on its own, separate from the PR - it should then help in both cases.
• Better understanding of this should help fix Music abruptly stops during game startup, is fine when returning from a world #2364, Menu music restarts when interacting with the preview button (huh!) #1743 and Downloaded modules lack input mappings (module scanning) #2384. Probably some other stuff too. It also would help lay the foundation for further enhancements to configuring a world.