MDEV-31749 sporadic assert in MDEV-30619 new test

If the workers of a parallel replica are busy (potentially with long
queues), but the SQL thread has no events left to distribute (so it
goes idle), then the next event that comes from the primary will
update mi->last_master_timestamp with its timestamp, even if the
workers have not yet finished.

This patch changes the parallel replica logic which updates
last_master_timestamp after idling from using solely sql_thread_caught_up
(added in MDEV-29639) to using the latter with rli queued/dequeued
event counters.
That is, if  the queued count is equal to the dequeued count, it
means all events have been processed and the replica is considered
idle when the driver thread has also distributed all events.

Low level details of the commit include
- to make a more generalized test for Seconds_Behind_Master on
  the parallel replica, rpl_delayed_parallel_slave_sbm.test
  is renamed to rpl_parallel_sbm.test for this purpose.
- pause_sql_thread_on_next_event usage was removed
  with the MDEV-30619 fixes. Rather than remove it, we adapt it
  to the needs of this test case
- added test case to cover SBM spike of relay log read and LMT
  update that was fixed by MDEV-29639
- rpl_seconds_behind_master_spike.test is made to use
  the negate_clock_diff_with_master debug eval.

Reviewed By:
============
Andrei Elkin <andrei.elkin@mariadb.com>