Fix CreateWithLogicalSize() to set correct scale in wxMSW too

Unlike under Mac (see previous commit), this never worked correctly in
wxMSW at all, only SetScaleFactor() could be used to change the scale
factor of the bitmaps there.

Fix this and make CreateWithLogicalSize(..., scale) result in
GetScaleFactor() returning the same scale for the resulting bitmap, as
expected, under MSW too.

Also add a unit test verifying that this holds.

tests/graphics/bmpbundle.cpp

@@ -172,8 +172,13 @@ TEST_CASE("BitmapBundle::Scale", "[bmpbundle][scale]")
     // This is not a wxBitmapBundle test, strictly speaking, but check that
     // setting scale factor works correctly for bitmaps, as wxBitmapBundle does
     // this internally.
-    wxBitmap bmp(16, 16);
-    bmp.SetScaleFactor(2);
+    wxBitmap bmp;
+    bmp.CreateWithLogicalSize(8, 8, 2);
+#ifdef wxHAS_DPI_INDEPENDENT_PIXELS
+    CHECK( bmp.GetLogicalSize() == wxSize(8, 8) );
+#endif
+    CHECK( bmp.GetDIPSize() == wxSize(8, 8) );
+    CHECK( bmp.GetSize() == wxSize(16, 16) );
     CHECK( bmp.GetScaleFactor() == 2 );
 
     wxBitmap bmp2(bmp);