fix: generate predictable UUIDs for offline accounts

Signed-off-by: Sefa Eyeoglu <contact@scrumplex.net>

launcher/minecraft/auth/MinecraftAccount.h

@@ -98,6 +98,8 @@ public: /* construction */
     static MinecraftAccountPtr loadFromJsonV2(const QJsonObject &json);
     static MinecraftAccountPtr loadFromJsonV3(const QJsonObject &json);
 
+    static QUuid uuidFromUsername(QString username);
+
     //! Saves a MinecraftAccount to a JSON object and returns it.
     QJsonObject saveToJson() const;