Added support for selecting multiple images in the insert dialog. Fixed an issue with inserting multiple images via DnD.
When inserting a single image into a shape with a background or onto another existing image - they are replaced.
If insert multiple images into a shape or onto an existing image - they are inserted instead of being replaced.
To achieve this, SetMultiInsertState(...) and isMultiInsert() methods have been added for DnD, and the boolean
variable isMultiInsert is passed for insertion via lcl_InsertGraphic(...).
Change-Id: Id299be0112ffe0bdf1aafb534edbfb216859dbf4
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/200891
Tested-by: Jenkins
Reviewed-by: Roman Kuznetsov <antilibreoffice@gmail.com>