Improve print preview and printing with high DPI

All print related scaling is based on 96DPI, so always let the printing contexts return this,
and also adjust the font to this DPI.

src/osx/core/printmac.cpp

@@ -30,6 +30,7 @@
 
 #include "wx/printdlg.h"
 #include "wx/paper.h"
+#include "wx/display.h"
 #include "wx/osx/printdlg.h"
 
 #include <stdlib.h>
@@ -746,10 +747,7 @@ bool wxMacPrintPreview::Print(bool interactive)
 
 void wxMacPrintPreview::DetermineScaling()
 {
-    int screenWidth , screenHeight ;
-    wxDisplaySize( &screenWidth , &screenHeight ) ;
-
-    wxSize ppiScreen = wxGetDisplayPPI();
+    wxSize ppiScreen = wxDisplay::GetStdPPI();
     wxSize ppiPrinter( 72 , 72 ) ;
 
     m_previewPrintout->SetPPIScreen( ppiScreen.x , ppiScreen.y ) ;