Expose number of FINISHING queries

Sometimes a query may spend a sifnificant amount of time in FINISHING
state if query result is large and all tasks already finished execution.
This is possible with fault tolerant execution.

core/trino-main/src/main/java/io/trino/dispatcher/DispatchManager.java

@@ -58,6 +58,7 @@
 import static com.google.common.base.Preconditions.checkArgument;
 import static com.google.common.collect.ImmutableList.toImmutableList;
 import static io.airlift.concurrent.Threads.daemonThreadsNamed;
+import static io.trino.execution.QueryState.FINISHING;
 import static io.trino.execution.QueryState.QUEUED;
 import static io.trino.execution.QueryState.RUNNING;
 import static io.trino.spi.StandardErrorCode.QUERY_TEXT_TOO_LARGE;
@@ -330,6 +331,14 @@ public long getRunningQueries()
                 .count();
     }
 
+    @Managed
+    public long getFinishingQueries()
+    {
+        return queryTracker.getAllQueries().stream()
+                .filter(query -> query.getState() == FINISHING)
+                .count();
+    }
+
     @Managed
     public long getProgressingQueries()
     {