feat(filesystem): add custom save path support per game

- Add custom_save_paths map to Settings::Values
- Implement ReadCustomSavePathValues and SaveCustomSavePathValues in Config
- Update CreateSaveDataFactory to check for custom save paths
- Support per-game title ID save path overrides

Signed-off-by: Zephyron <zephyron@citron-emu.org>

src/common/settings.h

@@ -683,6 +683,9 @@ struct Values {
     // Cheats
     // Key: build_id (hex string), Value: set of disabled cheat names
     std::map<std::string, std::set<std::string>> disabled_cheats;
+
+    // Custom Save Paths
+    std::map<u64, std::string> custom_save_paths;
 };
 
 extern Values values;