Merge branch 'ui-locale'

Add wxUILocale class providing functionality which can be implemented
portably for all major platforms, including macOS, and doesn't force
the change of the global C locale, unlike wxLocale.

See https://github.com/wxWidgets/wxWidgets/pull/2464

include/wx/generic/spinctlg.h

@@ -430,8 +430,6 @@ private:
     void DoSetDigitsAndUpdate(unsigned digits);
 
 
-    wxString m_format;
-
     wxDECLARE_DYNAMIC_CLASS(wxSpinCtrlDouble);
 };