Printing improvements: GetPageInfo() gets called after the DC has

Printing improvements: GetPageInfo() gets called after the DC has
been set and after OnPreparePrinting() has been called so it can
report the number of pages accurately; doesn't try to set
number of pages in print dialog, in common with other Windows apps;
wxHTML easy printing's preview shows number of pages
correctly; preview scrollbars are set correctly; keyboard navigation
improved

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@22263 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775