Hardcore mode

[CI09]

Brief Description of What This PR Does

This PR adds hardcore mode - removes standard saving from game together with quicksaves and in place of auto-saves a save is performed that writes into one save name selected upon save creation.

Related Issues

Progress Checklist

Note: before starting this checklist the PR should be marked as non-draft.

• PR author has checked that this PR works as intended and doesn't
  break existing features:
  https://wiki.revolutionarygamesstudio.com/wiki/Testing_Checklist
  (this is important as to not waste the time of Thrive team
  members reviewing this PR)
• Initial code review passed (this and further items should not be checked by the PR author)
• Functionality is confirmed working by another person (see above checklist link)
• Final code review is passed and code conforms to the
  styleguide.

Before merging all CI jobs should finish on this PR without errors, if
there are automatically detected style issues they should be fixed by
the PR author. Merging must follow our
styleguide.

[HexapodPhilosopher]

No bugs found. It is lacking a save on returning to the main menu, though. I was able to revert a bit by using that.

[hhyyrylainen]

I didn't check but this mode should also suppress the warning for exiting without saving as this should force the save when exiting so that warning is not incorrectly shown.

[hhyyrylainen]

This needs more bulletproofing against players exploiting the fact that the game doesn't save when exiting in this mode before I think this is a polished enough feature to include in the game.

[HexapodPhilosopher]

Also, wouldn't it make sense to include the checkbox for this in the Difficulty settings, rather than Misc? It's where most people would look for it.

[hhyyrylainen]

What's the current progress on this? Last I checked this was very brittle in terms of how well it saves and keeps the player from very easily cheating in the difficulty mode.

[CI09]

I got stuck at saving upon leaving so help would be useful. It's not mandatory feature though so you know...

[hhyyrylainen]

That's fine, I'll just take this off the list of PRs I need to review.

[github-actions]

This PR has been inactive for a while and as such is being marked
stale. This PR will be automatically closed if this stays stale
for a while.

If this is still being worked on / will probably resume work at
some point please feel free to continue working on this and reopen
this in case this was already automatically closed.

[revolutionary-bot]

We are currently in feature freeze until the next release.
If your PR is not just a simple fix, then it may take until the release to get reviewed and merged.