add jest, run it with ESModules, add example test, include in github workflow

Author: jeyj0

.github/workflows/check_js.yml

@@ -17,4 +17,6 @@ jobs:
     - run: cd lib/IHP/DataSync && npm install
       name: 'Install NPM Packages'
     - run: cd lib/IHP/DataSync && npm run typecheck
-      name: 'Typechecking DataSync modules'
+      name: 'Typechecking DataSync modules'
+    - run: cd lib/IHP/DataSync && npm run test
+      name: 'Testing DataSync modules'

lib/IHP/DataSync/ihp-querybuilder.test.js

@@ -0,0 +1,5 @@
+import { query } from './ihp-querybuilder';
+
+test('1+1=2', () => {
+    expect(1 + 1).toBe(2)
+})