Phase 3 tracking issue

[bvisness]

The entry requirements for phase 3 are:

• Test suite has been updated to cover the feature in its forked repo.
• The test suite should run against some implementation, though it need not be the reference interpreter.
• Updates on the actual spec document and reference interpreter are NOT yet required (but can happen earlier).

The natural path forward for us is to add tests, implement it in wasm-tools, and implement (and pass) the test suite in SpiderMonkey.

The following design issues should be addressed first:

• Deduplicating import type bytes in addition to import module names #7