The extra information for the graphic selection is now formatted
according to JSON syntax so that is easier to parse.

Information for allowing the client to performa constrained dragging
of a pie segment is appended when needed to the graphic selection
message.

A polygon approximation of the pie segment in svg format is attached
too to the graphic selection message.

Core now is able to handle a specific msg from the client with data
about the new pie segment offset computed by the client on drag end.
This information is dispatched by the chart controller to a specific
method: executeDispatch_LOKPieSegmentDragging.

Change-Id: I42e7742508fa3a453383bf7b95e47df169f24834
Reviewed-on: https://gerrit.libreoffice.org/70568Reviewed-by: Marco Cecchetti <mrcekets@gmail.com>
Tested-by: Marco Cecchetti <mrcekets@gmail.com>