Don't modify source map when parsing composite runtime field (#89114)

When calling RuntimeField.parseRuntimeFields() for fields defined in the
search request, we need to wrap the Map containing field definitions in another
Map that supports value removal, so that we don't inadvertently remove the
definitions from the root request. CompositeRuntimeField was not doing this
extra wrapping, which meant that requests that went to multiple shards and
that therefore parsed the definitions multiple times would throw an error
complaining that the fields parameter was missing, because the root request
had been modified.

Author: romseygeek

docs/changelog/89114.yaml

@@ -0,0 +1,5 @@
+pr: 89114
+summary: Don't modify source map when parsing composite runtime field
+area: Mapping
+type: bug
+issues: []

modules/runtime-fields-common/src/yamlRestTest/resources/rest-api-spec/test/runtime_fields/111_search_time_composite.yml

@@ -0,0 +1,36 @@
+---
+setup:
+  - do:
+      indices.create:
+        index: test
+        body:
+          settings:
+            number_of_shards: 2
+            number_of_replicas: 0
+  - do:
+      bulk:
+        index: test
+        refresh: true
+        body: |
+          {"index":{}}
+          {"A":2}
+
+---
+"search-time composite across multiple shards":
+  - do:
+      search:
+        index: test
+        body:
+          query:
+            term:
+              "r.shouldReturn" : true
+          runtime_mappings:
+            r:
+              type: composite
+              fields:
+                shouldReturn:
+                  type: boolean
+              script:
+                source: "emit('shouldReturn',true)"
+
+  - match: {hits.total.value: 1}

server/src/main/java/org/elasticsearch/index/mapper/CompositeRuntimeField.java

@@ -17,6 +17,7 @@
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Collections;
+import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Objects;
@@ -85,7 +86,12 @@ protected RuntimeField createRuntimeField(MappingParserContext parserContext) {
                 name,
                 lookup -> factory.newFactory(name, script.get().getParams(), lookup)
             );
-            Map<String, RuntimeField> runtimeFields = RuntimeField.parseRuntimeFields(fields.getValue(), parserContext, builder, false);
+            Map<String, RuntimeField> runtimeFields = RuntimeField.parseRuntimeFields(
+                new HashMap<>(fields.getValue()),
+                parserContext,
+                builder,
+                false
+            );
             return new CompositeRuntimeField(name, getParameters(), runtimeFields.values());
         }
     });
@@ -118,11 +124,6 @@ public XContentBuilder toXContent(XContentBuilder builder, Params params) throws
         for (FieldMapper.Parameter<?> parameter : parameters) {
             parameter.toXContent(builder, includeDefaults);
         }
-        builder.startObject("fields");
-        for (RuntimeField subfield : subfields) {
-            subfield.toXContent(builder, params);
-        }
-        builder.endObject();
         builder.endObject();
         return builder;
     }