chore: migrate remaining tests to Mocha (#5616)

This commit updates all the non-Puppeteer unit tests to run using Mocha and then deletes the custom test runner framework from this repository. The documentation has also been updated.

mocha-config/base.js

@@ -0,0 +1,3 @@
+module.exports = {
+  reporter: 'dot',
+};

mocha-config/browser-bundle-tests.js

@@ -0,0 +1,6 @@
+const base = require('./base');
+
+module.exports = {
+  ...base,
+  spec: 'utils/browser/*.spec.js',
+};

mocha-config/doclint-tests.js

@@ -0,0 +1,6 @@
+const base = require('./base');
+
+module.exports = {
+  ...base,
+  spec: 'utils/doclint/**/*.spec.js',
+};

mocha-config/puppeteer-unit-tests.js

@@ -0,0 +1,8 @@
+const base = require('./base');
+
+module.exports = {
+  ...base,
+  file: ['./test/mocha-utils.js'],
+  spec: 'test/*.spec.js',
+  timeout: process.env.PUPPETEER_PRODUCT === 'firefox' ? 15 * 1000 : 10 * 1000,
+};