wtdb: supply commited update count to PostEvaluateFilterFn

In this commit, we adjust the PostEvaluateFilterFn to also take in a
count representing the number of committed updates (ie, persisted
un-acked updates) that the session has. This will be made use of in an
upcoming commit.

watchtower/wtclient/client.go

@@ -67,8 +67,8 @@ func (c *client) genSessionFilter(
 
 // ExhaustedSessionFilter constructs a wtdb.ClientSessionFilterFn filter
 // function that will filter out any sessions that have been exhausted.
-func ExhaustedSessionFilter() wtdb.ClientSessionFilterFn {
-	return func(session *wtdb.ClientSession) bool {
+func ExhaustedSessionFilter() wtdb.ClientSessWithNumCommittedUpdatesFilterFn {
+	return func(session *wtdb.ClientSession, _ uint16) bool {
 		return session.SeqNum < session.Policy.MaxUpdates
 	}
 }