MB-58961: Make ActiveStream::curChkSeqno weakly-monotonic type

In follow-up patches we are fixing a bug where the monotonicity is
violated.

Change-Id: I8325f8822a0f616519e0630762b570b4dfa02e76
Reviewed-on: https://review.couchbase.org/c/kv_engine/+/198890
Well-Formed: Restriction Checker
Tested-by: Build Bot <[email protected]>
Reviewed-by: Dave Rigby <[email protected]>

Author: paolococchi

engines/ep/src/dcp/active_stream.h

@@ -847,7 +847,7 @@ class ActiveStream : public Stream,
     std::atomic<uint64_t> lastSentSeqnoAdvance;
 
     //! The last known seqno pointed to by the checkpoint cursor
-    std::atomic<uint64_t> curChkSeqno;
+    AtomicWeaklyMonotonic<uint64_t, ThrowExceptionPolicy> curChkSeqno;
 
     /*
      * The next snapshot start that we will send (set when we set