Although this follows a very different code path, copy the ww8
import idea of "consuming" the bookmark of a BOOK_FIELD.

This is particularly important for textcontrols, especially
since LO keeps duplicating bookmarks as it adds another
bookmark for the field name at each save.

Existing unit tests that this matches are fdo53985.docx and
tdf111964.docx. I expected more, but apparently most fields
don't contain or represent any bookmarks.

This patch is for import only. A followup patch stops
the creation of duplicate bookmarks during export.

Change-Id: I1e11980e52dc523393fd6d621191228d676e9a17
Reviewed-on: https://gerrit.libreoffice.org/61615
Tested-by: Jenkins
Reviewed-by: Justin Luth <justin_luth@sil.org>