Don't intern leafName in Mapper.Builder (elastic#119554) (elastic#119603)

We shouldn't intern in the builder already.
It's redundant since we'll be interning the mapper name
when we actually build the mapper instance anyway and introduces a
non-trivial slowdown into mapper serialization because we create
temporary builders during serialization that never turn into
concrete instances.

Author: original-brownbear

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

@@ -107,9 +107,8 @@ public abstract static class Builder {
 
         private String leafName;
 
-        @SuppressWarnings("this-escape")
         protected Builder(String leafName) {
-            setLeafName(leafName);
+            this.leafName = leafName;
         }
 
         public final String leafName() {
@@ -120,7 +119,7 @@ public final String leafName() {
         public abstract Mapper build(MapperBuilderContext context);
 
         void setLeafName(String leafName) {
-            this.leafName = internFieldName(leafName);
+            this.leafName = leafName;
         }
     }