Now that we know selections are sorted, we can get the set of selections
needing updating in log(n) time using a binary search, for modification
not changing the line count, this makes updating selections run in log(n)
instead of n.
this avoids a lot of unnecessary (add|remove)_change_listener as
creating temporary Selections do not call that anymore.
Use can choose between a SelectionList which or a DynamicSelectionList
depending on wethear the buffer will be modified or not during the
selections lifetime.
