Fix per-game config values leaking across titles

[vivekstills]

Per-Game Config Bug Fix

The Problem

Settings from one game were incorrectly persisting when loading a different game. When Game A defined configuration values in its TOML file and Game B did not override those same settings, Game B would still use Game A's values. This occurred because the cvar system retained the previous game's game_config_value_ state without clearing it before loading the next title's configuration.

The Solution

This patch adds a cleanup step that resets all per-game overrides before loading a new title's configuration. Each game now starts from global and default values unless it explicitly defines its own overrides.

Changes Made

1. Added reset method to config variables

   • Implemented ResetGameConfigValue in the IConfigVar interface
   • Clears the cached game_config_value_ pointer
   • Triggers UpdateValue() to recalculate the setting using the standard precedence: default → global → CLI → game-specific

2. Added system-wide reset function

   • Created ResetGameConfigValues() in src/xenia/config.cc
   • Iterates through all registered config variables and resets each one

3. Modified game config loading

   • Updated LoadGameConfig() to call ResetGameConfigValues() at the start
   • Ensures each title loads from a clean state before applying its TOML overrides

Impact

• Eliminates unintended inheritance of config values between games
• Ensures per-title configurations operate independently
• Resolves issues where settings from a previous session would affect subsequent titles

[vivekstills]

@benvanik @DrChat @Triang3l
Could you please review this PR when you get time?

[BorealisEcho]

@vivekstills Xenia-project master is no longer maintained as far as I know. If you want to help, go to xenia-canary.