Remove --harness requirement from stubbing

[celinval]

Description of changes:

The compiler can now generate code for different combinations of harnesses with and without stubs. For that, we implemented a little state machine that may execute the underlying rust compiler multiple times. The first run is always for harnesses that don't have stub, while the subsequent runs are for harnesses with stubs.

Resolved issues:

Resolves #1841

Related RFC:

#1809

Call-outs:

1. I have not changed how the compiler handles Tests and PublicFns reachability yet to minimize the changes in this PR. I created Finish refactoring on how we handle the metadata file for Tests and PubFns #2493 to capture that work.
2. We should also optimize the number of compiler sessions we execute when multiple harnesses use the same set of stubs. For simplicity, we only handle one harness at a time in this PR: Reduce the compilation overhead for harnesses with the same set of stubs. #2494
   3. Keeping this as a draft since we are blocked waiting for Simplify compiler queries structure (internal) #2486. Once this change goes through, I'll drop the first commit.

Testing:

• How is this change tested? New tests

• Is this a refactor change? Kinda

Checklist

• Each commit message has a non-empty body, explaining why the change was made
• Methods or procedures are documented
• Regression or unit tests are included, or existing tests cover the modified code
• My PR is restricted to a single feature or bugfix

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 and MIT licenses.

[zhassan-aws]

Neat! Thanks @celinval! I have a few comments.

[zhassan-aws]

Good to go