Fix error message about ChangeWindowMessageFilter() on startup under XP.

Use wxDynamicLibrary::RawGetSymbol() (from inside wxDL_INIT_FUNC() macro)
instead of GetSymbol() to avoid the error message which was given every time a
new wxFrame was created after wxTaskBarButton changes under XP as
ChangeWindowMessageFilter() function is not available in it.

Also simplify the code a little and don't make pfnChangeWindowMessageFilter
static, we don't need to keep it around.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@77681 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Implement strike-through support in wxFont in wxOSX.

Implement support for this attribute in wxOSX too.

Closes #16547.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@77682 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775