add test diagnostics test for internal error

javascript/ql/integration-tests/all-platforms/diagnostics/internal-error/src/my_failure.ts

@@ -0,0 +1,17 @@
+type Output<K, S extends any[]> = {
+  (...args: S): any;
+};
+
+declare function createThing<K extends string, S extends any[]>(
+  type: K,
+  fn: (...args: S) => any
+): Output<K, S>;
+
+const one = createThing("one", () => ({}));
+
+const two = createThing("two", () => ({}));
+
+const three = createThing("three", (cursor: string) => null);
+const four = createThing("four", (error: number) => null);
+
+type Events = Array<typeof one | typeof two | typeof three | typeof four>;