And, while at it, rewrite the layout algorithm to operate on blocks of
overlapping events, and segmented columns. Like the month view row,
layouts blocks are invalidated at any point in time, but recalculated
immediately before a relayout happens.
The reason for doing such a massive rewrite while in the middle of the
port to GListModel is because it's easier to handle GListModel data
with this approach, than with the previous approach of storing it all
in a GcalRangeTree.
Closes: https://gitlab.gnome.org/GNOME/gnome-calendar/-/issues/1153
Part-of: <https://gitlab.gnome.org/GNOME/gnome-calendar/-/merge_requests/742>
mindonwarp