Add tests for a full `bankai build`

[goto-bus-stop]

This adds some basic tests for bankai build, specifically things that have been broken in the past:

• bankai build app/ and bankai build app/index.js should both output to the same directory app/dist by default
• bankai build outputs dynamic bundles created with split-require

• [x] tests pass
• [x] tests and/or benchmarks are included