Various wxFont fixes in wxQt

Implement point/pixel size accessors correctly.

Implement support for strike-through fonts.

Also implement DoSetNativeFontInfo() for wxQt.

Make wxFont unit test pass by accounting for Qt-specific aspects.

Closes https://github.com/wxWidgets/wxWidgets/pull/1113

src/common/fontcmn.cpp

@@ -439,8 +439,7 @@ bool wxFontBase::operator==(const wxFont& font) const
             // in wxGTK1 GetPixelSize() calls GetInternalFont() which uses
             // operator==() resulting in infinite recursion so we can't use it
             // in that port
-            // in wxQT, GetPixelSize is too slow to be used here
-#if (!defined(__WXGTK__) || defined(__WXGTK20__)) && !defined(__WXQT__)
+#if (!defined(__WXGTK__) || defined(__WXGTK20__))
             GetPixelSize() == font.GetPixelSize() &&
 #endif
             GetFamily() == font.GetFamily() &&