implemeent a reduction approach, which is good at finding virtual
methods that only themselves or their virtual partners.

The accessibility GetVisArea stuff is dead since
    commit 891e41fa
    Date:   Wed Apr 4 11:23:22 2018 +0200
    dead code in AccessibleTextHelper_Impl::UpdateVisibleChildren

Change-Id: I78d9d8bca585ecec8394f2c3fe2baa93db0e58f5
Reviewed-on: https://gerrit.libreoffice.org/60912
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>