feat(chat): when stderr is not empty, do not discard stdout when exit code is 0

[Davidyz]

Description

Currently, the tool class discard stdout when stderr is not empty even if the exit code is 0. In the real world a lot of programs/libraries (in my case, VectorCode) use stderr for warnings that don't actually terminate the command. The current way in which stdout and stderr are handled caused false negatives in some cases (outputs with useful information get thrown away).

I'm not sure if it's appropriate to call both output.error and output.success. I simply copied the code under elseif not vim.tbl_isempty(stdout) then here.

Checklist

• I've read the contributing guidelines and have adhered to them in this PR
• I've updated the README and/or relevant docs pages
• I've run make docs to update the vimdoc pages

[olimorris]

Great inclusion, thanks.

I'm currently working on refactoring the tools class. Hopefully finished tomorrow. No changes to functionality but it needs splitting out into separate files, so hopefully easier to understand.