CppEditor: Extract CppLocalRenaming
Now CppEditorWidget is much less convoluted with the local rename mode.
This class can be reused since there is no dependency on
CPPEditorWidget.
Change-Id: If513e59a03214cf9f2e3831f7e3616c001e1f036
Reviewed-by:
Erik Verbruggen <erik.verbruggen@digia.com>