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/CMakeLists.txt

@@ -76,6 +76,8 @@ add_executable(citra-qt
     game_list.cpp
     game_list.h
     game_list_p.h
+    game_list_worker.cpp
+    game_list_worker.h
     hotkeys.cpp
     hotkeys.h
     main.cpp