gflib.ts: generate source map, which is helpful for debugging

src/runtime/typescript/js/gflib.js

@@ -1160,3 +1160,4 @@ if (!String.prototype.includes) {
         }
     });
 }
+//# sourceMappingURL=gflib.js.map

src/runtime/typescript/tsconfig.json

@@ -5,7 +5,8 @@
     "strict": true,
     "noImplicitAny": true,
     "removeComments": true,
-    "outDir": "js"
+    "outDir": "js",
+    "sourceMap": true
   },
   "compileOnSave": true
 }