* SwTOXBaseSection::Update(): refactor this to *first* collect the info
  from the document (creating CrossRefHeadingBookmark as a side effect)
  and *then* do the node deletion/insertion of the ToX itself

* add new SwUndoUpdateIndex class for the update itself; it does 3 of
  the 4 required steps, the last one is done by a SwUndoDelSection that
  is already created when the original title section is deleted

* SwUndoInsSection::RedoImpl() for a ToX should not Update the ToX
  because that's the job of SwUndoUpdateIndex

* SwUndoSaveSection::RestoreSection()/MoveFromUndoNds() need to create
  frames for the moved nodes; not sure why other users of
  RestoreSection() don't do this currently so add a flag

* SwUndoSaveContent::MoveToUndoNds() should *always* delete frames;
  seriously, why would leaving frames alive ever be a good idea?

* SwUndoSaveSection::SaveSection() should not delete the surrounding
  section node of the ToX, so add a flag to prevent it

This fixes tdf#123313, the SwUndoInsBookmark are now appended at the
right time.

This should fix the crash in i#42807 properly.

In order to fix these bugs, implementing the feature requested in
tdf#38703 was necessary.

Change-Id: Ia976a118eb81ca37b0c48678825a1f5cd4031789
Reviewed-on: https://gerrit.libreoffice.org/71323
Tested-by: Jenkins
Reviewed-by: Michael Stahl <Michael.Stahl@cib.de>