crimson/os/pg_map: allow multiple shards to create new pg mappings at the same time

crimson/os/pg_map: allow multiple shards to create new pg mappings at the same time

Also:
* Better detections in case of inconsistent racings, such as:
  * The new mapping is creating towards different cores.
  * Mapping creation is racing with its eracing.
  * Multiple shards are erasing the same mapping at the same time.
* Add more logs to debug in case of unexpected issues.

Fixes: https://tracker.ceph.com/issues/64934
Fixes: https://tracker.ceph.com/issues/64009
Signed-off-by: Yingxin Cheng <yingxin.cheng@intel.com>