Implement the text selection IM queries. Never seen them, but
since the text querying code is already there, it's easy to
extend to include the selection. Anchor is the non-cursor
position of the selection and should return the cursor in case
of not selected text.

Change-Id: I0e49a8593a5a6c6268395857748b5fc304372210
Reviewed-on: https://gerrit.libreoffice.org/71797
Tested-by: Jenkins
Reviewed-by: Jan-Marek Glogowski <glogow@fbihome.de>