Fix NumberFieldMapper Referencing its Own Builder (#77131)

Investigating the heap use of mapper instances I found this.
It seems quite a bit of overhead for these instances goes into
the builder field. In other mappers we retain the script service
and the script outright, so I did the same thing here to make these
instances a little smaller.

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

@@ -81,7 +81,7 @@ public static class Builder extends FieldMapper.Builder {
 
         private final Parameter<Number> nullValue;
 
-        private final Parameter<Script> script = Parameter.scriptParam(m -> toType(m).builder.script.get());
+        private final Parameter<Script> script = Parameter.scriptParam(m -> toType(m).script);
         private final Parameter<String> onScriptError = Parameter.onScriptErrorParam(m -> toType(m).onScriptError, script);
         private final Parameter<Boolean> dimension;
 
@@ -1084,7 +1084,6 @@ public boolean isDimension() {
         }
     }
 
-    private final Builder builder;
     private final NumberType type;
 
     private final boolean indexed;
@@ -1097,6 +1096,8 @@ public boolean isDimension() {
     private final boolean ignoreMalformedByDefault;
     private final boolean coerceByDefault;
     private final boolean dimension;
+    private final ScriptCompiler scriptCompiler;
+    private final Script script;
 
     private NumberFieldMapper(
             String simpleName,
@@ -1116,7 +1117,8 @@ private NumberFieldMapper(
         this.coerceByDefault = builder.coerce.getDefaultValue().value();
         this.scriptValues = builder.scriptValues();
         this.dimension = builder.dimension.getValue();
-        this.builder = builder;
+        this.scriptCompiler = builder.scriptCompiler;
+        this.script = builder.script.getValue();
     }
 
     boolean coerce() {
@@ -1203,7 +1205,7 @@ protected void indexScriptValues(SearchLookup searchLookup, LeafReaderContext re
 
     @Override
     public FieldMapper.Builder getMergeBuilder() {
-        return new Builder(simpleName(), type, builder.scriptCompiler, ignoreMalformedByDefault, coerceByDefault)
+        return new Builder(simpleName(), type, scriptCompiler, ignoreMalformedByDefault, coerceByDefault)
             .dimension(dimension).init(this);
     }
 }