intended to replace the existing methods that return mutable ref

And add the clang rewriter I will use to do most of the work.

Change-Id: If00be13da5c16c07671cedbcfea21528bac33c8a
Reviewed-on: https://gerrit.libreoffice.org/49430Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>