Ensure dynamicMapping updates are handled in insertion order (#103047) (#103083)

The switch to holding dynamic fields in a hashmap effectively randomizes their iteration order. This can be troublesome when building the mapping update required by these updates. When iterating in an unknown order, recursing to the leaf mapper can occur many times `O(n^2)`. However, starting with insertion order, it will occur only `O(n)` times.

closes: #103011

Author: benwtrent

docs/changelog/103047.yaml

@@ -0,0 +1,5 @@
+pr: 103047
+summary: Ensure `dynamicMapping` updates are handled in insertion order
+area: Mapping
+type: bug
+issues: []

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

@@ -22,8 +22,8 @@
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Collections;
-import java.util.HashMap;
 import java.util.HashSet;
+import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
@@ -166,9 +166,9 @@ protected DocumentParserContext(
             mappingParserContext,
             source,
             new HashSet<>(),
-            new HashMap<>(),
+            new LinkedHashMap<>(),
             new HashSet<>(),
-            new HashMap<>(),
+            new LinkedHashMap<>(),
             new ArrayList<>(),
             null,
             null,