We do not consolidate positions when removing sections to prevent
failing requests while deleting chapters. Collection length can, thus,
not be used to ensure unique position attributes.

REDMINE-20217

REDMINE-20217

Chapter positions are needed to sort the global sections
collection. Ensure parent model is already set during initial sort,
such that previous sections can be determined correctly right from the
start.

Otherwise, the outline displays an incorrect transition after
inserting a section since the previous section can not yet be used to
determine available transitions.

REDMINE-20217

When inserting a section at the beginning of the entry, we need to
update the transition of the previously first section. Also the
section might no longer be the active section, even though
currentSectionIndex did not change.

REDMINE-20217