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/Config/PropertiesDialog.cpp

@@ -13,11 +13,15 @@
 #include "DolphinQt2/Config/InfoWidget.h"
 #include "DolphinQt2/Config/PatchesWidget.h"
 #include "DolphinQt2/Config/PropertiesDialog.h"
+#include "UICommon/GameFile.h"
 
-PropertiesDialog::PropertiesDialog(QWidget* parent, const GameFile& game) : QDialog(parent)
+PropertiesDialog::PropertiesDialog(QWidget* parent, const UICommon::GameFile& game)
+    : QDialog(parent)
 {
-  setWindowTitle(
-      QStringLiteral("%1: %2 - %3").arg(game.GetFileName(), game.GetGameID(), game.GetLongName()));
+  setWindowTitle(QStringLiteral("%1: %2 - %3")
+                     .arg(QString::fromStdString(game.GetFileName()),
+                          QString::fromStdString(game.GetGameID()),
+                          QString::fromStdString(game.GetLongName())));
   QVBoxLayout* layout = new QVBoxLayout();
 
   QTabWidget* tab_widget = new QTabWidget(this);
@@ -39,7 +43,7 @@ PropertiesDialog::PropertiesDialog(QWidget* parent, const GameFile& game) : QDia
   tab_widget->addTab(gecko, tr("Gecko Codes"));
   tab_widget->addTab(info, tr("Info"));
 
-  if (DiscIO::IsDisc(game.GetPlatformID()))
+  if (DiscIO::IsDisc(game.GetPlatform()))
   {
     FilesystemWidget* filesystem = new FilesystemWidget(game);
     tab_widget->addTab(filesystem, tr("Filesystem"));