Add readCurrentRevision helper

Summary: To read the current revision written into the manifest at build-time.

Reviewed By: danielbuechele

Differential Revision: D14454983

fbshipit-source-id: adad7d85dbf410701d2f8601bfccbcfbc0f30dff

src/utils/__tests__/packageMetadata.node.js

@@ -0,0 +1,13 @@
+/**
+ * Copyright 2018-present Facebook.
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ * @format
+ */
+
+import {readCurrentRevision} from '../packageMetadata.js';
+
+test('readCurrentRevision does not return something meaningful in dev mode', async () => {
+  const ret = await readCurrentRevision();
+  expect(ret).toBeUndefined();
+});