Implement wxTextEntryBase::Clear() using Remove() instead of SetValue()

This avoids problems with SetValue() overrides not doing the intended thing
(for example wxComboBox). See #16654

include/wx/textentry.h

@@ -57,7 +57,7 @@ public:
 
     virtual void Replace(long from, long to, const wxString& value);
     virtual void Remove(long from, long to) = 0;
-    virtual void Clear() { SetValue(wxString()); }
+    virtual void Clear() { Remove(0, -1); }
     void RemoveSelection();