Remove strong ordering of annotation ranges
After a long chat with Lilith Halfner, we've come to the conclusion that
the range-based ordering applied to annotations, while nice for making
some otherwise O(n) code O(log n) and O(n^2) code O(n), is actually
assuming too much about how annotations are used and interact with each
other. Removing all assumptions about ordering, and giving annotation
order primacy seems like the most sensible thing to do, even if it makes
a few bits of the code less algorithmically "nice".
As a consequence, we also get rid of annotatedstring_optimize!. Specific
producers/consumers of annotated text will know what assumptions can be
made to compress/optimise the annotations used, and are thus best suited
to do so themselves. The one exception to this is probably when writing
to an AnnotatedIOBuffer, here adding a specific optimisation to
_insert_annotations! probably makes sense, and will be explored soon.
