Avoid importing .json files (#12759)

* Avoid importing `.json` files

* Use ESold in babel.config.json

* Use `import/extensions` eslint plugin

lib/package-json.d.ts

@@ -0,0 +1,8 @@
+// NOTE: This global .d.ts file can be included with
+//    /// <reference path="../../../lib/package-json.d.ts" />
+// in .ts files using the PACKAGE_JSON macro.
+
+declare const PACKAGE_JSON: {
+  name: string;
+  version: string;
+};

lib/package-json.js.flow

@@ -0,0 +1,4 @@
+declare var PACKAGE_JSON: {
+  name: string;
+  version: string;
+};