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/DolphinQt2.vcxproj

@@ -97,7 +97,6 @@
     <QtMoc Include="Debugger\NewBreakpointDialog.h" />
     <QtMoc Include="Debugger\RegisterWidget.h" />
     <QtMoc Include="Debugger\WatchWidget.h" />
-    <QtMoc Include="GameList\GameFile.h" />
     <QtMoc Include="GameList\GameList.h" />
     <QtMoc Include="GameList\GameListModel.h" />
     <QtMoc Include="GameList\GameTracker.h" />
@@ -250,8 +249,6 @@
     <ClCompile Include="Debugger\RegisterWidget.cpp" />
     <ClCompile Include="Debugger\WatchWidget.cpp" />
     <ClCompile Include="GCMemcardManager.cpp" />
-    <ClCompile Include="GameList\GameFile.cpp" />
-    <ClCompile Include="GameList\GameFileCache.cpp" />
     <ClCompile Include="GameList\GameList.cpp" />
     <ClCompile Include="GameList\GameListModel.cpp" />
     <ClCompile Include="GameList\GameTracker.cpp" />
@@ -271,6 +268,7 @@
     <ClCompile Include="NetPlay\PadMappingDialog.cpp" />
     <ClCompile Include="QtUtils\DoubleClickEventFilter.cpp" />
     <ClCompile Include="QtUtils\ElidedButton.cpp" />
+    <ClCompile Include="QtUtils\ImageConverter.cpp" />
     <ClCompile Include="QtUtils\ListTabWidget.cpp" />
     <ClCompile Include="QtUtils\WindowActivationEventFilter.cpp" />
     <ClCompile Include="QtUtils\AspectRatioWidget.cpp" />
@@ -311,9 +309,9 @@
     <ClInclude Include="Config\Mapping\WiimoteEmuMotionControl.h" />
     <ClInclude Include="Config\RegisterColumn.h" />
     <ClInclude Include="Config\RegisterWidget.h" />
-    <ClInclude Include="GameList\GameFileCache.h" />
     <ClInclude Include="QtUtils\BlockUserInputFilter.h" />
     <ClInclude Include="QtUtils\ElidedButton.h" />
+    <ClInclude Include="QtUtils\ImageConverter.h" />
     <ClInclude Include="QtUtils\ListTabWidget.h" />
     <ClInclude Include="Resources.h" />
     <ClInclude Include="Settings\GameCubePane.h" />