The default case is that all managers have assistants/employees, so
nodes under a manager can only use the horizontal space under the
manager to avoid overlapping.

But in case the previous / next sibling of the manager have no child
nodes (assistant/employee) then we can use that space to make the child
nodes larger. This improves readability of the chart's text a lot and
brings the layout closer to what PowerPoint does for the same input.

Handle all this in the hierChild algorithm, i.e. the container for a
list of assistants or a list of employees, which means "parent" in this
context always refers to a manager node.

Change-Id: Ib4125ea2a113339ab7bbcd78e43c5d204f442996
Reviewed-on: https://gerrit.libreoffice.org/66504Reviewed-by: Miklos Vajna <vmiklos@collabora.com>
Tested-by: Jenkins