Resolve ambiguity in multiple inheritance of function GetPropertyByLabel in wxPGPage.

In wxPropertyGridPage class derived from wxPropertyGridPageState and wxPropertyGridInterface, function GetPropertyByLabel is inherited from both base classes.
To resolve this ambiguity, function defined in wxPGInterface is introduced in wxPGPage through 'using-declaration'.
(This is a temporary fix and finally GetPropertyByLabel function should be removed from wxPropertyGridPageState.)

See #15251.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@76925 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/propgrid/propgridpagestate.h

@@ -556,8 +556,11 @@ public:
 
     wxPropertyCategory* GetPropertyCategory( const wxPGProperty* p ) const;
 
+#ifdef WXWIN_COMPATIBILITY_3_0
+    wxDEPRECATED_MSG("don't refer directly to wxPropertyGridPageState::GetPropertyByLabel")
     wxPGProperty* GetPropertyByLabel( const wxString& name,
                                       wxPGProperty* parent = NULL ) const;
+#endif // WXWIN_COMPATIBILITY_3_0
 
     wxVariant DoGetPropertyValues( const wxString& listname,
                                    wxPGProperty* baseparent,
@@ -690,6 +693,10 @@ protected:
     bool PrepareToAddItem( wxPGProperty* property,
                            wxPGProperty* scheduledParent );
 
+    /** Returns property by its label. */
+    wxPGProperty* BaseGetPropertyByLabel( const wxString& label,
+                                      wxPGProperty* parent = NULL ) const;
+
     /** If visible, then this is pointer to wxPropertyGrid.
         This shall *never* be NULL to indicate that this state is not visible.
     */