[shell] script to generate WASM database code

Summary:
Script downloads SQLite code (if it does not exist) and generates two files:

• CommQueryExecutor.js which is glue code in ES6 format, will be imported to JS code
• CommQueryExecutor.wasm which is actual implementation

Test Plan:

• run script and check if files are created properly
• run second time and check if SQLite assets are not re-downloaded

Reviewers: jon, michal, tomek

Reviewed By: jon

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D8390