Unify ISOFile (wx) with GameFile (Qt) and put it in UICommon

The original reason I wanted to do this was so that we can replace
the Android-specific code with this in the future, but of course,
just deduplicating between DolphinWX and DolphinQt2 is nice too.

Fixes:

- DolphinQt2 showing the wrong size for split WBFS disc images.

- DolphinQt2 being case sensitive when checking if a file is a DOL/ELF.

- DolphinQt2 not detecting when a Wii banner has become available
after the game list cache was created.

Removes:

- DolphinWX's ability to load PNGs as custom banners. But it was
already rather broken (see https://bugs.dolphin-emu.org/issues/10365
and https://bugs.dolphin-emu.org/issues/10366). The reason I removed
this was because PNG decoding relied on wx code and we don't have any
good non-wx/Qt code for loading PNG files right now (let's not use
SOIL), but we should be able to use libpng directly to implement PNG
loading in the future.

- DolphinQt2's ability to ignore a cached game if the last modified
time differs. We currently don't have a non-wx/Qt way to get the time.

Source/Core/DolphinWX/GameListCtrl.h

@@ -16,7 +16,12 @@
 #include "Common/ChunkFile.h"
 #include "Common/Event.h"
 #include "Common/Flag.h"
-#include "DolphinWX/ISOFile.h"
+#include "UICommon/GameFileCache.h"
+
+namespace UICommon
+{
+class GameFile;
+}
 
 class wxEmuStateTip : public wxTipWindow
 {
@@ -46,8 +51,8 @@ public:
   ~GameListCtrl();
 
   void BrowseForDirectory();
-  const GameListItem* GetISO(size_t index) const;
-  const GameListItem* GetSelectedISO() const;
+  const UICommon::GameFile* GetISO(size_t index) const;
+  const UICommon::GameFile* GetSelectedISO() const;
 
   static bool IsHidingItems();
 
@@ -80,9 +85,7 @@ private:
   void SetColors();
   void RefreshList();
   void RescanList();
-  void DoState(PointerWrap* p, u32 size = 0);
-  bool SyncCacheFile(bool write);
-  std::vector<const GameListItem*> GetAllSelectedISOs() const;
+  std::vector<const UICommon::GameFile*> GetAllSelectedISOs() const;
 
   // events
   void OnRefreshGameList(wxCommandEvent& event);
@@ -124,9 +127,9 @@ private:
     std::vector<int> emu_state;
   } m_image_indexes;
 
-  // Actual backing GameListItems are maintained in a background thread and cached to file
-  std::vector<std::shared_ptr<GameListItem>> m_cached_files;
-  // Locks the list, not the contents
+  // Actual backing GameFiles are maintained in a background thread and cached to file
+  UICommon::GameFileCache m_cache;
+  // Locks the cache object, not the shared_ptr<GameFile>s obtained from it
   std::mutex m_cache_mutex;
   Core::TitleDatabase m_title_database;
   std::mutex m_title_database_mutex;
@@ -134,7 +137,7 @@ private:
   Common::Event m_scan_trigger;
   Common::Flag m_scan_exiting;
   // UI thread's view into the cache
-  std::vector<std::shared_ptr<GameListItem>> m_shown_files;
+  std::vector<std::shared_ptr<const UICommon::GameFile>> m_shown_files;
 
   int m_last_column;
   int m_last_sort;