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/DolphinQt2/MenuBar.h

@@ -5,13 +5,12 @@
 #pragma once
 
 #include <array>
+#include <memory>
 #include <string>
 
 #include <QMenu>
 #include <QMenuBar>
 
-#include "DolphinQt2/GameList/GameFile.h"
-
 namespace Core
 {
 enum class State;
@@ -22,6 +21,11 @@ namespace DiscIO
 enum class Region;
 };
 
+namespace UICommon
+{
+class GameFile;
+}
+
 class MenuBar final : public QMenuBar
 {
   Q_OBJECT
@@ -89,7 +93,7 @@ signals:
   void ExportRecording();
   void ShowTASInput();
 
-  void SelectionChanged(QSharedPointer<GameFile> game_file);
+  void SelectionChanged(std::shared_ptr<const UICommon::GameFile> game_file);
   void RecordingStatusChanged(bool recording);
   void ReadOnlyModeChanged(bool read_only);
 
@@ -120,7 +124,7 @@ private:
   void CheckNAND();
   void NANDExtractCertificates();
 
-  void OnSelectionChanged(QSharedPointer<GameFile> game_file);
+  void OnSelectionChanged(std::shared_ptr<const UICommon::GameFile> game_file);
   void OnRecordingStatusChanged(bool recording);
   void OnReadOnlyModeChanged(bool read_only);
   void OnDebugModeToggled(bool enabled);