When the window is resized, the viewport is automatically reset.

This resolves lots of confusion around resizable windows.  Most people don't expect a viewport to be implicitly set when the renderer is created and then not to be reset to the window size if the window is resized.

Added common test command line parameters --logical WxH and --scale N to test the render logical size and scaling APIs.

include/SDL_test_common.h

@@ -69,6 +69,9 @@ typedef struct
     int window_minH;
     int window_maxW;
     int window_maxH;
+    int logical_w;
+    int logical_h;
+    float scale;
     int depth;
     int refresh_rate;
     int num_windows;