Achievements: Preserve hardcore mode when toggling encore/spectator/unofficial settings

[mariobob]

Toggling "Enable Encore Mode", "Enable Spectator Mode", or "Test Unofficial Achievements" while a game is running no longer disables hardcore mode.

Problem

Previously, changing any of these three settings during gameplay would trigger a full Shutdown() + Initialize() cycle, which disabled hardcore mode until the game was reset.

This change allows players to toggle these options mid-session without losing hardcore mode.

Solution

Instead of destroying and recreating the rc_client, we can reload the game achievement state by calling ClearGameInfo() + BeginLoadGame(). This unloads and reloads the game on the existing client, preserving the hardcore mode state while still properly applying the settings changes (e.g., Encore Mode correctly resets achievement unlock states and can be done multiple times in a session).

Screenshots

Before	After

[stenzek]

Probably should save/restore the cheevo state, but eh, whatever.. not like this is being toggled often.

[mariobob]

@stenzek almost forgot about that. I'd really like this to work properly, so I've added save/restore state here: #3663

It will allow players to re-earn the same achievements multiple times in a single session if they want to, without resetting achievement/leaderboard progress. (probably won't be used often, but I'd like to use it :P)