JavaScript: Consolidate ModuleImportNode tests.

Note that `CustomImport.ql` is still separate since it customises the standard library and would hence influennce other tests.

javascript/ql/test/library-tests/ModuleImportNodes/moduleImportProp.qll

@@ -0,0 +1,5 @@
+import javascript
+
+query predicate test_moduleImportProp(string path, string prop, DataFlow::PropRead res) {
+  res = DataFlow::moduleImport(path).getAPropertyRead(prop)
+}