Allow using wxDEFAULT as font size in wxOSX.

Using wxDEFAULT as the font size in wxOSX resulted in creating 70pt font,
change this to use the normal font size instead for compatibility with the
other platforms.

Also allow using -1 as wxDEFAULT for compatibility with wxGTK, see #12541.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@73884 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Add wxFontInfo class to allow using named parameters for wxFont creation.

This helper class allows to create wxFonts using shorter and more readable
code, e.g.

	wxFont font(12, wxFONTFLAG_DEFAULT,
		    wxFONTSTYLE_NORMAL, wxFONTWEIGHT_NORMAL, true,
		    "DejaVu Sans");

can now be written simply as

	wxFont font(wxFontInfo(12).FaceName("DejaVu Sans").Underlined());

Remove the ctor from font flags added in r70445 as it's not needed any longer
now that we have this one and adding it resulted in compilation errors in the
existing code which compiled with 2.8 because of ambiguities between that ctor
and wxFont(int size, int family, int style, int weight. bool underlined, ...)
one, e.g.

	wxFont(12, wxFONTFAMILY_SWISS, wxNORMAL, wxNORMAL)

didn't compile any more but it does compile again now.

See #9907.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@73885 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775