Fix documentation for QPrinter::PrinterResolution

Documentation omitted the fact that PrinterResolution is not checked in QPdfPrintEngine code at all, and would end up using the default value set in the code. Pick-to: 6.8 6.10 Fixes: QTBUG-133410 Change-Id: I2424b46acf10db6da7d8e02b31132e6e0c273976 Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io> Reviewed-by: Sami Varanka <sami.varanka@qt.io> Reviewed-by: Titta Heikkala <titta.heikkala@qt.io>

Author: TomiKorpipaa

src/printsupport/kernel/qprinter.cpp

@@ -335,11 +335,11 @@ class QPrinterPagedPaintDevicePrivate : public QPagedPaintDevicePrivate
  lower quality output than HighResolution and should only be used
  for drafts.
 
- \value PrinterResolution This value is deprecated. It is
- equivalent to ScreenResolution on Unix and HighResolution on
- Windows and Mac. Due to the difference between ScreenResolution
- and HighResolution, use of this value may lead to non-portable
- printer code.
+ \value PrinterResolution This value is deprecated. For printers,
+ it is equivalent to ScreenResolution on Unix and HighResolution
+ on Windows and macOS. For PDF printing, it is not supported and
+ may result in undefined behavior. Using this value can lead to
+ non-portable printer code.
 
  \value HighResolution On Windows, sets the printer resolution to that
  defined for the printer in use. For PDF printing, sets the