Add TAP tests to check replication slot advance during the checkpoint

Add TAP tests to check replication slot advance during the checkpoint

The new tests verify that logical and physical replication slots are still
valid after an immediate restart on checkpoint completion when the slot was
advanced during the checkpoint.

This commit introduces two new injection points to make these tests possible:

* checkpoint-before-old-wal-removal - triggered in the checkpointer process
  just before old WAL segments cleanup;
* logical-replication-slot-advance-segment - triggered in
  LogicalConfirmReceivedLocation() when restart_lsn was changed enough to
  point to the next WAL segment.

Discussion: https://postgr.es/m/flat/1d12d2-67235980-35-19a406a0%4063439497
Author: Vitaly Davydov 
Author: Tomas Vondra 
Reviewed-by: Alexander Korotkov 
Reviewed-by: Amit Kapila 
Backpatch-through: 17