Save memory on numeric sig terms when not top (#56789)

This saves memory when running numeric significant terms which are not
at the top level by merging its collection into numeric terms and relying
on the optimization that we made in #55873.

Author: nik9000

docs/reference/search/profile.asciidoc

@@ -782,7 +782,7 @@ This yields the following aggregation profile output:
       {
         "aggregations" : [
           {
-            "type" : "LongTermsAggregator",
+            "type" : "NumericTermsAggregator",
             "description" : "my_scoped_agg",
             "time_in_nanos" : 195386,
             "breakdown" : {
@@ -796,6 +796,7 @@ This yields the following aggregation profile output:
               "collect_count" : 4
             },
             "debug": {
+              "result_strategy": "long_terms",
               "total_buckets": 4
             }
           },
@@ -815,7 +816,7 @@ This yields the following aggregation profile output:
             },
             "children" : [
               {
-                "type" : "LongTermsAggregator",
+                "type" : "NumericTermsAggregator",
                 "description" : "my_level_agg",
                 "time_in_nanos" : 160329,
                 "breakdown" : {
@@ -829,6 +830,7 @@ This yields the following aggregation profile output:
                   "collect_count" : 4,
                 },
                 "debug": {
+                  "result_strategy": "long_terms",
                   "total_buckets": 4
                 }
               }
@@ -845,10 +847,10 @@ This yields the following aggregation profile output:
 // TESTRESPONSE[s/"id": "\[P6-vulHtQRWuD4YnubWb7A\]\[test\]\[0\]"/"id": $body.profile.shards.0.id/]
 
 From the profile structure we can see that the `my_scoped_agg` is internally 
-being run as a `LongTermsAggregator` (because the field it is aggregating, 
+being run as a `NumericTermsAggregator` (because the field it is aggregating, 
 `likes`, is a numeric field). At the same level, we see a `GlobalAggregator` 
 which comes from `my_global_agg`. That aggregation then has a child 
-`LongTermsAggregator` which comes from the second term's aggregation on `likes`.
+`NumericTermsAggregator` which comes from the second term's aggregation on `likes`.
 
 The `time_in_nanos` field shows the time executed by each aggregation, and is 
 inclusive of all children.  While the overall time is useful, the `breakdown` 

rest-api-spec/src/main/resources/rest-api-spec/test/search.aggregation/20_terms.yml

@@ -726,8 +726,8 @@ setup:
 ---
 "profiler":
   - skip:
-      version: " - 7.8.99"
-      reason: debug information added in 7.9.0
+      version: " - 7.99.99"
+      reason: debug information added in 7.9.0 (change backporting to 7.9.0)
   - do:
       bulk:
         index: test_1
@@ -782,7 +782,8 @@ setup:
                 field: number
   - match: { aggregations.n_terms.buckets.0.key: 1 }
   - match: { aggregations.n_terms.buckets.1.key: 3 }
-  - match: { profile.shards.0.aggregations.0.type: LongTermsAggregator }
+  - match: { profile.shards.0.aggregations.0.type: NumericTermsAggregator }
   - match: { profile.shards.0.aggregations.0.description: n_terms }
   - match: { profile.shards.0.aggregations.0.breakdown.collect_count: 4 }
+  - match: { profile.shards.0.aggregations.0.debug.result_strategy: long_terms }
   - match: { profile.shards.0.aggregations.0.debug.total_buckets: 2 }

server/src/internalClusterTest/java/org/elasticsearch/search/aggregations/bucket/SignificantTermsSignificanceScoreIT.java

@@ -195,7 +195,7 @@ public void testXContentResponse() throws Exception {
 
     }
 
-    public void testDeletesIssue7951() throws Exception {
+    public void testPopularTermManyDeletedDocs() throws Exception {
         String settings = "{\"index.number_of_shards\": 1, \"index.number_of_replicas\": 0}";
         assertAcked(prepareCreate(INDEX_NAME).setSettings(settings, XContentType.JSON)
                 .setMapping("text", "type=keyword", CLASS_FIELD, "type=keyword"));
@@ -237,7 +237,7 @@ public void testDeletesIssue7951() throws Exception {
                                 significantTerms("sig_terms")
                                         .field(TEXT_FIELD)
                                         .minDocCount(1)));
-        }else
+        } else
         {
             request = client().prepareSearch(INDEX_NAME)
                     .addAggregation(
@@ -477,8 +477,7 @@ public void testScriptScore() throws ExecutionException, InterruptedException, I
                             .subAggregation(significantText("mySignificantTerms", TEXT_FIELD)
                             .significanceHeuristic(scriptHeuristic)
                             .minDocCount(1).shardSize(2).size(2)));
-        }else
-        {
+        } else {
             request = client().prepareSearch(INDEX_NAME)
                     .addAggregation(terms("class").field(CLASS_FIELD)
                             .subAggregation(significantTerms("mySignificantTerms")

server/src/main/java/org/elasticsearch/search/aggregations/bucket/terms/DoubleTerms.java

@@ -39,7 +39,7 @@ public class DoubleTerms extends InternalMappedTerms<DoubleTerms, DoubleTerms.Bu
     public static final String NAME = "dterms";
 
     static class Bucket extends InternalTerms.Bucket<Bucket> {
-        private final double term;
+        double term;
 
         Bucket(double term, long docCount, InternalAggregations aggregations, boolean showDocCountError, long docCountError,
                 DocValueFormat format) {