Tests: TS: add back missing type checking

tsx does not run any type checking, hence a separate
tsc step is needed .

Also, fix resulting type issue caused by external lib types.

test/typescript/tsconfig.test.json

@@ -0,0 +1,7 @@
+{
+  "extends": "../../tsconfig.json",
+  "compilerOptions": {
+    "noEmit": true, // tested by tsx
+  },
+  "files": ["definitions.ts"]
+}