Blacklist the "tools-offset" action in the GUI, and only keep
"filters-offset", to avoid duplication. Update gimp:offset's
description, so that "filters-offset" gets a proper tool-tip.
(cherry picked from commit 42d4255262)
Add a new gimp:offset operation, which implements equivalent
functionality to gimp_drawable_offset(), in preparation for adding
an interactive offset tool.
To simplify things, add a GIMP_OFFSET_WRAP_AROUND value to the
GimpOffsetType enum, to avoid the need for a separate wrap-around
flag. This makes the gimp-drawable-offset procedure parameters a
little superfluous, but whatever.
(cherry picked from commit 40fefb6076)
