Defer buildling of plan description until retrieve time...

As the query collector always collects queries (and therefore builds
the plan description), we defer building it until the queries are
retrieved, instead of rebuilding it on every query invocation.

community/data-collector/src/main/java/org/neo4j/internal/collector/QueryCollector.java

@@ -114,7 +114,7 @@ public void endSuccess( ExecutingQuery query )
             QuerySnapshot snapshot = query.snapshot();
             queries.produce(
                     new TruncatedQuerySnapshot( snapshot.queryText(),
-                                                snapshot.queryPlan(),
+                                                snapshot.queryPlanSupplier(),
                                                 snapshot.queryParameters(),
                                                 snapshot.elapsedTimeMicros(),
                                                 snapshot.compilationTimeMicros(),

community/data-collector/src/main/java/org/neo4j/internal/collector/TruncatedQuerySnapshot.java

@@ -19,6 +19,8 @@
  */
 package org.neo4j.internal.collector;
 
+import java.util.function.Supplier;
+
 import org.neo4j.graphdb.ExecutionPlanDescription;
 import org.neo4j.values.AnyValue;
 import org.neo4j.values.SequenceValue;
@@ -51,14 +53,14 @@ class TruncatedQuerySnapshot
 {
     final int fullQueryTextHash;
     final String queryText;
-    final ExecutionPlanDescription queryPlan;
+    final Supplier<ExecutionPlanDescription> queryPlanSupplier;
     final MapValue queryParameters;
     final Long elapsedTimeMicros;
     final Long compilationTimeMicros;
     final Long startTimestampMillis;
 
     TruncatedQuerySnapshot( String fullQueryText,
-                            ExecutionPlanDescription queryPlan,
+                            Supplier<ExecutionPlanDescription> queryPlanSupplier,
                             MapValue queryParameters,
                             Long elapsedTimeMicros,
                             Long compilationTimeMicros,
@@ -67,7 +69,7 @@ class TruncatedQuerySnapshot
     {
         this.fullQueryTextHash = fullQueryText.hashCode();
         this.queryText = truncateQueryText( fullQueryText, maxQueryTextLength );
-        this.queryPlan = queryPlan;
+        this.queryPlanSupplier = queryPlanSupplier;
         this.queryParameters = truncateParameters( queryParameters );
         this.elapsedTimeMicros = elapsedTimeMicros;
         this.compilationTimeMicros = compilationTimeMicros;

community/data-collector/src/main/scala/org/neo4j/internal/collector/QueriesSection.scala

@@ -60,7 +60,8 @@ object QueriesSection {
       val snapshot = querySnapshots.next()
       val queryString = snapshot.queryText
       if (QUERY_FILTER.findFirstMatchIn(queryString).isEmpty) {
-        val snapshotList = queries.getOrElseUpdate(QueryKey(queryString, snapshot.fullQueryTextHash, snapshot.queryPlan), new QueryData())
+        val queryKey = QueryKey(queryString, snapshot.fullQueryTextHash, snapshot.queryPlanSupplier.get())
+        val snapshotList = queries.getOrElseUpdate(queryKey, new QueryData())
         snapshotList.invocations += SingleInvocation(snapshot.queryParameters,
                                                      snapshot.elapsedTimeMicros,
                                                      snapshot.compilationTimeMicros,

community/kernel/src/main/java/org/neo4j/kernel/api/query/ExecutingQuery.java

@@ -252,9 +252,9 @@ public String queryText()
         return queryText;
     }
 
-    public ExecutionPlanDescription planDescription()
+    public Supplier<ExecutionPlanDescription> planDescriptionSupplier()
     {
-        return planDescriptionSupplier.get();
+        return planDescriptionSupplier;
     }
 
     public MapValue queryParameters()

community/kernel/src/main/java/org/neo4j/kernel/api/query/QuerySnapshot.java

@@ -22,6 +22,7 @@
 import java.util.Collections;
 import java.util.List;
 import java.util.Map;
+import java.util.function.Supplier;
 import java.util.stream.Collectors;
 
 import org.neo4j.graphdb.ExecutionPlanDescription;
@@ -72,9 +73,9 @@ public String queryText()
         return query.queryText();
     }
 
-    public ExecutionPlanDescription queryPlan()
+    public Supplier<ExecutionPlanDescription> queryPlanSupplier()
     {
-        return query.planDescription();
+        return query.planDescriptionSupplier();
     }
 
     public MapValue queryParameters()