Include symtab2gb conversion in --only-codegen

[adpaco-aws]

Description of changes:

#957 will need more fixes and discussions to be enabled. In the meantime, this PR includes the symtab2gb conversion step in --only-codegen runs, so that Kani fails if the conversion from Kani-generated symbol tables to GotoC program is invalid.

Resolved issues:

Resolves #1584

Call-outs:

Testing:

• How is this change tested? Existing regression. Run locally the top 100 crates experiment, but it doesn't affect results.

• Is this a refactor change? No.

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.

[celinval]

It's awesome that it hasn't affected the top 100 crates results! Thanks

[adpaco-aws]

It's awesome that it hasn't affected the top 100 crates results! Thanks

Unfortunately, these results shouldn't be trusted: #1563

[celinval]

It's awesome that it hasn't affected the top 100 crates results! Thanks

Unfortunately, these results shouldn't be trusted: #1563

That's odd. I'm curious to know why that's the case.