Expand javadoc on NodeInfo

Move the javadoc from Node#info onto NodeInfo and make it clearer what
it's used for.

Author: alex-spies

x-pack/plugin/esql-core/src/main/java/org/elasticsearch/xpack/esql/core/tree/Node.java

@@ -307,16 +307,7 @@ protected final <E> T transformNodeProps(Class<E> typeToken, Function<? super E,
     }
 
     /**
-     * Return the information about this node.
-     * <p>
      * Normally, you want to use one of the static {@code create} methods to implement this.
-     * <p>
-     * For {@code QueryPlan}s, it is very important that
-     * the properties contain all of the expressions and references relevant to this node, and
-     * that all of the properties are used in the provided constructor; otherwise query plan
-     * transformations like
-     * {@code QueryPlan#transformExpressionsOnly(Function)}
-     * will not have an effect.
      */
     protected abstract NodeInfo<? extends T> info();
 

x-pack/plugin/esql-core/src/main/java/org/elasticsearch/xpack/esql/core/tree/NodeInfo.java

@@ -16,7 +16,16 @@
 import static java.util.Collections.unmodifiableList;
 
 /**
- * Information about a {@link Node}.
+ * All the information about a {@link Node} that is needed to recreate or modify it.
+ * <p>
+ * Allows us to perform traversals and transformations of query plans and expressions without resorting to reflection.
+ * <p>
+ * For {@code QueryPlan}s, it is very important that
+ * the properties contain all of the expressions and references relevant to this node, and
+ * that all the properties are used in the provided constructor; otherwise query plan
+ * transformations like
+ * {@code QueryPlan#transformExpressionsOnly(Function)}
+ * will not have an effect.
  * <p>
  * All the uses of this are fairly non-OO and we're looking
  * for ways to use this less and less.