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/ISOProperties/ISOProperties.h

@@ -15,8 +15,8 @@
 #include <wx/treebase.h>
 
 #include "Common/IniFile.h"
-#include "DolphinWX/ISOFile.h"
 #include "DolphinWX/PatchAddEdit.h"
+#include "UICommon/GameFile.h"
 
 class ActionReplayCodesPanel;
 class CheatWarningMessage;
@@ -52,9 +52,9 @@ wxDECLARE_EVENT(DOLPHIN_EVT_CHANGE_ISO_PROPERTIES_TITLE, wxCommandEvent);
 class CISOProperties : public wxDialog
 {
 public:
-  CISOProperties(const GameListItem& game_list_item, wxWindow* parent, wxWindowID id = wxID_ANY,
-                 const wxString& title = _("Properties"), const wxPoint& pos = wxDefaultPosition,
-                 const wxSize& size = wxDefaultSize,
+  CISOProperties(const UICommon::GameFile& game_list_item, wxWindow* parent,
+                 wxWindowID id = wxID_ANY, const wxString& title = _("Properties"),
+                 const wxPoint& pos = wxDefaultPosition, const wxSize& size = wxDefaultSize,
                  long style = wxDEFAULT_DIALOG_STYLE | wxRESIZE_BORDER);
   virtual ~CISOProperties();
 
@@ -141,7 +141,7 @@ private:
   void OnCheatCodeToggled(wxCommandEvent& event);
   void OnChangeTitle(wxCommandEvent& event);
 
-  const GameListItem m_open_gamelist_item;
+  const UICommon::GameFile m_open_gamelist_item;
 
   IniFile m_gameini_default;
   IniFile m_gameini_local;