Dispatch IntervalIndex.argsort to IntervalArray
cc @jschendel thoughts on if we can do better in the non-ascending/"quicksort" case?
any timings on the various cases? lgtm. perf timings? havent done any timings, am hoping to get guidance from @jschendel on the remaining cases Closing to clear the queue, will revisit, still hoping @jschendel can weigh in on how best to handle the remaining cases.