[web] implement test c++ class

Summary:
This class will be removed, adding this here to iterate over compiling code to WASM and share a general idea.
I will start adding proper implementation after some changes to the native code.

Depends on D8375

Test Plan: N/A

Reviewers: jon, tomek, michal

Reviewed By: tomek

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D8389