[web] add function to retrieve WASM module

Summary:
Making sure that module is now typed in Flow, and making it easier to retrieve the module (will be helpful in tests later).

Depends on D8545

Test Plan:

1. flow
2. Check if result is still logged

Reviewers: michal, tomek

Reviewed By: michal

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D8547