Allow -u to accept a username string in addition to index, and suppress the User selector even if settings requires it to be shown for one instance only.

src/yuzu/main.h

@@ -523,6 +523,8 @@ private:
     std::unique_ptr<EmuThread> emu_thread;
     // The path to the game currently running
     QString current_game_path;
+    // Whether a user was set on the command line (skips UserSelector if it's forced to show up)
+    bool user_flag_cmd_line = false;
 
     bool auto_paused = false;
     bool auto_muted = false;