refactor: add a commit-msg git hook to check commit messages (#22969)

The commit command will fail if the commit message header does not follow the
Angular convetions as defined in /CONTRIBUTING.md.

You can force the commit by adding the `--no-verify` option.

NOTE:
You should remove all unused hooks (in <angular>/.git/hooks) before running
`yarn` so that husky hooks are installed correctly.

PR Close #22969

scripts/git/commit-msg.js

@@ -0,0 +1,31 @@
+#! /usr/bin/env node
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+// git commit-msg hook to check the commit message against Angular conventions
+// see `/CONTRIBUTING.md` for mode details.
+
+'use strict';
+
+const fs = require('fs');
+const checkMsg = require('../../tools/validate-commit-message');
+const msgFile = process.env['GIT_PARAMS'];
+
+let isValid = true;
+
+if (msgFile) {
+    const commitMsg = fs.readFileSync(msgFile, {encoding: 'utf-8'});
+    const firstLine = commitMsg.split('\n')[0];
+    isValid = checkMsg(firstLine);
+
+    if (!isValid) {
+        console.error('\nCheck CONTRIBUTING.md at the root of the repo for more information.')
+    }
+}
+
+process.exit(isValid ? 0 : 1);