feat(dev-infra): create rebase-pr tool in ng-dev (#37055)

Creates a tool in ng-dev which rebases a PR automatically and pushes
the rebase commits back to the PR.  This is meant to be a replacement
to the local merge script currently in the repo and currently has
feature parity.

PR Close #37055

dev-infra/pr/rebase/cli.ts

@@ -0,0 +1,35 @@
+/**
+ * @license
+ * Copyright Google LLC 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
+ */
+
+import {Arguments, Argv} from 'yargs';
+
+import {rebasePr} from './index';
+
+/** URL to the Github page where personal access tokens can be generated. */
+export const GITHUB_TOKEN_GENERATE_URL = `https://github.com/settings/tokens`;
+
+/** Builds the rebase pull request command. */
+export function buildRebaseCommand(yargs: Argv) {
+  return yargs.option('github-token', {
+    type: 'string',
+    description: 'Github token. If not set, token is retrieved from the environment variables.'
+  });
+}
+
+/** Handles the rebase pull request command. */
+export async function handleRebaseCommand(args: Arguments) {
+  const githubToken = args.githubToken || process.env.GITHUB_TOKEN || process.env.TOKEN;
+  if (!githubToken) {
+    console.error('No Github token set. Please set the `GITHUB_TOKEN` environment variable.');
+    console.error('Alternatively, pass the `--github-token` command line flag.');
+    console.error(`You can generate a token here: ${GITHUB_TOKEN_GENERATE_URL}`);
+    process.exit(1);
+  }
+
+  await rebasePr(args.prNumber, githubToken);
+}