refactor(core): update `noSideEffects()` to return the result of the inner function (#35769)

This is useful for propagating return values without them being converted to a string. It still provides the same guarantees to Closure, which will assume that the function invoked is pure and can be tree-shaken accordingly.

PR Close #35769

packages/core/src/util/closure.ts

@@ -15,6 +15,6 @@
  * to something which is retained otherwise the call to `noSideEffects` will be removed by closure
  * compiler.
  */
-export function noSideEffects(fn: () => void): string {
-  return '' + {toString: fn};
-}
+export function noSideEffects<T>(fn: () => T): T {
+  return {toString: fn}.toString() as unknown as T;
+}