reorder GetLabel(), GetLabelText(), SetLabel() and SetLabelText() function declaratio...

reorder GetLabel(), GetLabelText(), SetLabel() and SetLabelText() function declarations, implementations and relative documentations.

Add wxStaticTextBase::GetLabelWithoutMarkup() and use it in the wxMSW implementation of wxStaticText::SetLabel() to close bug #11446; the function RemoveMarkup() which was previously used in fact could not check for presence/absence of wxST_MARKUP style since it's a static function.

Add wxStaticTextBase::SetLabelText() functions for symmetry with wxControlBase::SetLabelText()

Add test unit for both wxControl::*Label* and wxStaticText::*Label* functions.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@63733 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775