util: add 'none' style to styleText

For cases where the style is not needed but code still calls styleText
unconditionally, this adds a `none` style that not not apply any styling
to the text.

Author: jasnell

doc/api/util.md

@@ -2483,6 +2483,8 @@ console.log(
 );
 ```
 
+The special format value `none` applies no additional styling to the text.
+
 The full list of formats can be found in [modifiers][].
 
 ## Class: `util.TextDecoder`

lib/util.js

@@ -104,6 +104,7 @@ let internalDeepEqual;
  * @returns {string}
  */
 function escapeStyleCode(code) {
+  if (code === undefined) return '';
   return `\u001b[${code}m`;
 }
 
@@ -139,6 +140,7 @@ function styleText(format, text, { validateStream = true, stream = process.stdou
   let left = '';
   let right = '';
   for (const key of formatArray) {
+    if (key === 'none') continue;
     const formatCodes = inspect.colors[key];
     // If the format is not a valid style, throw an error
     if (formatCodes == null) {

test/parallel/test-util-styletext.js

@@ -75,6 +75,8 @@ assert.strictEqual(
   styled,
 );
 
+assert.strictEqual(util.styleText('none', 'test'), 'test');
+
 const fd = common.getTTYfd();
 if (fd !== -1) {
   const writeStream = new WriteStream(fd);