Set colours and fonts for all elements of the generic wxSearchCtrl.

Derive generic wxSearchCtrl from wxCompositeWindow<> to ensure that calls to
its Set{Fore,Back}groundColour() are propagated to all its children, otherwise
they applied only to the composite control itself but not e.g. its text part.

Also update the bitmaps when the background colour changes to ensure that it
appears as transparent.

Closes #13428.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@68911 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/srchctrl.h

@@ -26,10 +26,11 @@
     // no native version, use the generic one
     #define wxUSE_NATIVE_SEARCH_CONTROL 0
 
+    #include "wx/compositewin.h"
     #include "wx/containr.h"
 
     class WXDLLIMPEXP_CORE wxSearchCtrlBaseBaseClass
-        : public wxNavigationEnabled<wxControl>,
+        : public wxCompositeWindow< wxNavigationEnabled<wxControl> >,
           public wxTextCtrlIface
     {
     };