JetBrains: Fix JavaScript console errors

Created by: philipp-spiess

Fixes #35934 (closed)

There were two issues:

1. The indicateFinishedLoading case in the switch statement was not returning and thus falling through to the error case.
2. The JS side of the bridge is built to always have a return string that can be deserialized. So instead of returning nothing we are now returning an empty object like we expect on the JS side.

Test plan

App preview:

• Web
• Storybook

Check out the client app preview documentation to learn more.