osd: Reduce the amount of status invalidations when rolling shards forwards during...

osd: Reduce the amount of status invalidations when rolling shards forwards during peering

Currently stats invalidations happen during peering when rolling forward shards.
We can reduce this so we only invalidate the stats when we don't have any other shards at the version we want to roll the stats forwards to.
In the cases where we have a shard with the stats at the correct version, we use those stats instead of invalidating.
If we do not have any shards with the correct version of stats, we do the invalidate as before.
We also add a check to ensure that we don't use stats from a non-primary shard if the head of the log is a partial write, to prevent incorrect stats in fast ec.

Signed-off-by: Jon Bailey <jonathan.bailey1@ibm.com>