As commit b1cd83c6 (fix crash loading
ooo#93570-3.doc, 2014-07-04) notes, the way how we map WW8 CP indexes to
sw character positions is working only in the very simple cases.

However, to do that properly, we need a way to store the start position
of an annotation mark before we create it, so add a
RES_FLTR_ANNOTATIONMARK that can do so.

Change-Id: I7cb3564621803fef9a76edaac48773cab7649ee8