logd: ensure LogBufferElement mSequence is monotonic

- Improves accuracy of -t/-T '<timestamp>' behavior when out of order
  arrival of entries messes with mSequence as the list will now have
  monotonic sequence numbers enforced.
- Out of order time entries still remain because of reader requiring
  the ability to receive newly arrived old entries.
- -t/-T '<timestamp>' can still quit backward search prematurely
  because an old entry lands later in the list.
- Adjust insert in place algorithm from two loops of scan placement
  and then limit against watermark, into one that does all of that
  plus iteratively swap update the sequence numbers to set
  monotonicity.  Side effect will be that the read lock (which is
  actually the LogTimes lock) will be held longer while we search
  for a placement above the youngest LogTimes watermark.  We need
  to hold the read (LogTimes) lock because we may be altering the
  sequence numbers affecting -t/-T '<timestamp>' search.

Test: gTest logd-unit-tests liblog-unit-tests logcat-unit-tests
Bug: 35373582
Change-Id: I79a385fc149bac2179128b53d4c8f71e429181ae