test: enable importHelpers for UMD builds (#36989)

This is a workaround for a TS 3.9 regression https://github.com/microsoft/TypeScript/issues/38501 where the emitted `__exportStar` helpers have a missing semi-colon at the end of the unnamed function, when targetting UMD, and causes the following runtime error `Uncaught TypeError: (intermediate value)(…) is not a function`.

This is because the anonymous `__exportStar` function will be invoked with the function on the next like as the parameter which is subsequently invoking whatever was returned.

To get around this TS bug, add `importHelpers: true` in your tsconfig. This also, is recommanded to avoid multiple copies of the same helper being inlined, which might cause increase in bundle size.

PR Close #36989

integration/bazel/src/tsconfig.json

@@ -1,5 +1,6 @@
 {
   "compilerOptions": {
+    "importHelpers": true,
     "experimentalDecorators": true,
     "lib": [
       "dom",

packages/examples/upgrade/tsconfig-build.json

@@ -1,5 +1,6 @@
 {
   "compilerOptions": {
+    "importHelpers": true,
     "lib": ["dom", "es2015"],
     "types": ["angular"]
   }