yuzu: Move GameListWorker to its own source files

This has gotten sufficiently large enough to warrant moving it to its
own source files. Especially given it dumps the file_sys headers around
code that doesn't use it for the most part.

This'll also make it easier to introduce a type alias for the
compatibility list, so a large unordered_map type declaration doesn't
need to be specified all the time (we don't want to propagate the
game_list_p.h include via the main game_list.h header).

src/citra_qt/game_list.h

@@ -5,6 +5,7 @@
 #pragma once
 
 #include <unordered_map>
+#include <QMenu>
 #include <QString>
 #include <QWidget>
 #include "common/common_types.h"