[ES|QL] AST query and mutation APIs for metadata fields (elastic#195364)

## Summary

Partially addresses elastic#191812

This PR implements some generic ES|QL AST mutation APIs and specifically
APIs for working with `FROM` command `METADATA` fields:

- `from.metadata.list()` — List all `METADATA` fields.
- `from.metadata.find()` — Find a `METADATA` field by name.
- `from.metadata.removeByPredicate()` — Remove a `METADATA` field
by matching a predicate.
- `from.metadata.remove()` — Remove a `METADATA` field by name.
- `from.metadata.insert()` — Insert a `METADATA` field.
- `from.metadata.upsert()` — Insert `METADATA` field, if it does
not exist.

### Checklist

Delete any items that are not applicable to this PR.

- [x] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios

### For maintainers

- [x] This was checked for breaking API changes and was [labeled
appropriately](https://www.elastic.co/guide/en/kibana/master/contributing.html#kibana-release-notes-process)

(cherry picked from commit a819d65)

packages/kbn-esql-ast/README.md

@@ -12,6 +12,7 @@ Contents of this package:
 - [`walker` — Contains the ES|QL AST `Walker` utility](./src/walker/README.md).
 - [`visitor` — Contains the ES|QL AST `Visitor` utility](./src/visitor/README.md).
 - [`pretty_print` — Contains code for formatting AST to text](./src/pretty_print/README.md).
+- [`mutate` — Contains code for traversing and mutating the AST.](./src/mutate/README.md).
 
 
 ## Demo

packages/kbn-esql-ast/index.ts

@@ -56,3 +56,5 @@ export {
 } from './src/pretty_print';
 
 export { EsqlQuery } from './src/query';
+
+export * as mutate from './src/mutate';

packages/kbn-esql-ast/src/builder/builder.ts

@@ -12,15 +12,17 @@
 import {
   ESQLAstComment,
   ESQLAstQueryExpression,
+  ESQLColumn,
   ESQLCommand,
+  ESQLCommandOption,
   ESQLDecimalLiteral,
   ESQLInlineCast,
   ESQLIntegerLiteral,
   ESQLList,
   ESQLLocation,
   ESQLSource,
 } from '../types';
-import { AstNodeParserFields, AstNodeTemplate } from './types';
+import { AstNodeParserFields, AstNodeTemplate, PartialFields } from './types';
 
 export namespace Builder {
   /**
@@ -38,16 +40,29 @@ export namespace Builder {
   });
 
   export const command = (
-    template: AstNodeTemplate<ESQLCommand>,
+    template: PartialFields<AstNodeTemplate<ESQLCommand>, 'args'>,
     fromParser?: Partial<AstNodeParserFields>
   ): ESQLCommand => {
     return {
       ...template,
       ...Builder.parserFields(fromParser),
+      args: template.args ?? [],
       type: 'command',
     };
   };
 
+  export const option = (
+    template: PartialFields<AstNodeTemplate<ESQLCommandOption>, 'args'>,
+    fromParser?: Partial<AstNodeParserFields>
+  ): ESQLCommandOption => {
+    return {
+      ...template,
+      ...Builder.parserFields(fromParser),
+      args: template.args ?? [],
+      type: 'option',
+    };
+  };
+
   export const comment = (
     subtype: ESQLAstComment['subtype'],
     text: string,
@@ -85,6 +100,19 @@ export namespace Builder {
       };
     };
 
+    export const column = (
+      template: Omit<AstNodeTemplate<ESQLColumn>, 'name' | 'quoted'>,
+      fromParser?: Partial<AstNodeParserFields>
+    ): ESQLColumn => {
+      return {
+        ...template,
+        ...Builder.parserFields(fromParser),
+        quoted: false,
+        name: template.parts.join('.'),
+        type: 'column',
+      };
+    };
+
     export const inlineCast = (
       template: Omit<AstNodeTemplate<ESQLInlineCast>, 'name'>,
       fromParser?: Partial<AstNodeParserFields>

packages/kbn-esql-ast/src/builder/types.ts

@@ -29,3 +29,5 @@ export type AstNodeTemplate<Node extends ESQLProperNode> = Omit<
   'type' | 'text' | 'location' | 'incomplete'
 > &
   Partial<Omit<Node, 'type'>>;
+
+export type PartialFields<T, K extends keyof T> = Omit<T, K> & Partial<Pick<T, K>>;

packages/kbn-esql-ast/src/mutate/README.md

@@ -0,0 +1,36 @@
+# Mutation API
+
+The ES|QL mutation API provides methods to navigate and modify the AST.
+
+
+## Usage
+
+For example, insert a `FROM` command `METADATA` field:
+
+```typescript
+import { parse, mutate, BasicPrettyPrinter } from '@elastic/esql';
+
+const { root } = parse('FROM index METADATA _lang');
+
+console.log([...mutate.commands.from.metadata.list(root)]); // [ '_lang' ]
+
+mutate.commands.from.metadata.upsert(root, '_id');
+
+console.log([...mutate.commands.from.metadata.list(root)]); // [ '_lang', '_id' ]
+
+const src = BasicPrettyPrinter.print(root);
+
+console.log(src); // FROM index METADATA _lang, _id
+```
+
+
+## API
+
+- `.commands.from.metadata.list()` — List all `METADATA` fields.
+- `.commands.from.metadata.find()` — Find a `METADATA` field by name.
+- `.commands.from.metadata.removeByPredicate()` — Remove a `METADATA`
+  field by matching a predicate.
+- `.commands.from.metadata.remove()` — Remove a `METADATA` field by name.
+- `.commands.from.metadata.insert()` — Insert a `METADATA` field.
+- `.commands.from.metadata.upsert()` — Insert `METADATA` field, if it does
+  not exist.

packages/kbn-esql-ast/src/mutate/commands/from/index.ts

@@ -0,0 +1,12 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the "Elastic License
+ * 2.0", the "GNU Affero General Public License v3.0 only", and the "Server Side
+ * Public License v 1"; you may not use this file except in compliance with, at
+ * your election, the "Elastic License 2.0", the "GNU Affero General Public
+ * License v3.0 only", or the "Server Side Public License, v 1".
+ */
+
+import * as metadata from './metadata';
+
+export { metadata };