Update stylelint to 14.0.1

This also upgrades PostCSS to 8.3.11.

DISABLE_THIRD_PARTY_CHECK=Updating Stylelint configuration
R=szuend@chromium.org

Bug: none
Change-Id: I606540b03509d7c6e73f3d490327cd4174e03d31
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/3259541
Reviewed-by: Simon Zünd <szuend@chromium.org>
Commit-Queue: Tim van der Lippe <tvanderlippe@chromium.org>

node_modules/postcss-syntax/stringify.js

@@ -1,20 +0,0 @@
-"use strict";
-
-function stringify (document) {
-	let stringify;
-	if (document instanceof require("./document")) {
-		stringify = docStringify;
-	} else {
-		stringify = document.source.syntax.stringify;
-	}
-	return stringify.apply(this, arguments);
-}
-
-function docStringify (document, builder) {
-	document.nodes.forEach((root, i) => {
-		builder(root.raws.beforeStart, root, "beforeStart");
-		root.source.syntax && root.source.syntax.stringify(root, builder);
-	});
-	builder(document.raws.afterEnd, document, "afterEnd");
-}
-module.exports = stringify;