fs: update jsdoc for filehandle.createWriteStream and appendFile

PR-URL: nodejs#51494
Reviewed-By: Luigi Pinca <[email protected]>
Reviewed-By: Deokjin Kim <[email protected]>

Author: Jungku Lee

lib/fs.js

@@ -2379,6 +2379,7 @@ function writeFileSync(path, data, options) {
  *   encoding?: string | null;
  *   mode?: number;
  *   flag?: string;
+ *   flush?: boolean;
  *   } | string} [options]
  * @param {(err?: Error) => any} callback
  * @returns {void}

lib/internal/fs/promises.js

@@ -365,6 +365,7 @@ class FileHandle extends EventEmitter {
    *   autoClose?: boolean;
    *   emitClose?: boolean;
    *   start: number;
+   *   highWaterMark?: number;
    *   flush?: boolean;
    *   }} [options]
    * @returns {WriteStream}