Windows GDK Support (#5830)

* Added GDK

* Simplfied checks in SDL_config_wingdk.h

* Added testgdk sample

* Added GDK readme

* Fixed error in merge of SDL_windows.h

* Additional GDK fixes

* OpenWatcom should not export _SDL_GDKGetTaskQueue

* Formatting fixes

* Moved initialization code into SDL_GDKRunApp

VisualC-GDK/tests/testsprite2/PackageLayout.xml

@@ -0,0 +1,9 @@
+<Package>
+  <Chunk Id="1000" Marker="Launch">
+    <FileGroup DestinationPath="." SourcePath="." Include="testsprite2.exe" />
+    <FileGroup DestinationPath="." SourcePath="." Include="MicrosoftGame.config" />
+    <FileGroup DestinationPath="." SourcePath="." Include="*.bmp" />
+    <FileGroup DestinationPath="." SourcePath="." Include="*.png" />
+    <FileGroup DestinationPath="." SourcePath="." Include="*.dll" />
+  </Chunk>
+</Package>