test: consider using existing shell test suites

[39555]

I read about oils and its extensive https://github.com/oils-for-unix/oils/wiki/Spec-Tests. It is similar to brush yaml files and contains a lot of scripts from real-world codebases. Maybe we could use it directly or auto-format it into YAML files.

The stats for different shells can be found here https://www.oilshell.org/release/0.7.pre11/test/spec.wwz/for-expr.html

[reubeno]

FYI, the recently merged PR ( #288 ) enables us to start using the basic input backend to run the upstream bash-completion test suite. That test suite, while focused on programmable completion, ends up being a good battery of compatibility tests due to how much complex bash-isms are used by bash-completion.

Would love to find the right way to run that suite regularly, and follow that pattern to bring online execution of other existing test suites (like the ones you mention).