JS: Add failing test for assigning a non-SourceNode to a type annotated-value

Author: asgerf

javascript/ql/test/library-tests/UnderlyingTypes/varAssignment.ts

@@ -0,0 +1,5 @@
+import * as express from 'express';
+
+function t1(e) {
+    var req: express.Request = e; // $ MISSING: hasUnderlyingType='express'.Request
+}