Move symtab2gb to codegen step

[danielsn]

Description of changes:

This is a draft PR to codegen all the way to goto-binary, not just symtab json. Should make the process faster and more parallel.

Resolved issues:

Resolves #ISSUE-NUMBER

Related RFC:

Call-outs:

• currently missing any error handling the original code had.
• currently not deleting the temporary files

Testing:

• How is this change tested?

• Is this a refactor change?

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.