support simultaneous full-text and github output

[cwastranis]

The github output format emits github "workflow commands", which the github UI
interprets and uses to annotate source files with the detected errors. These
commands are elided from the full workflow logs, which means that users looking
at these logs cannot see file and line information for pyrefly errors. It would
be ideal if pyrefly could emit both github and full-text output
simultaneously.

I'm happy to submit a PR for this (subject to my company approving the CLA), and
would appreciate some feedback on how to best proceed.

Some history I've found:

• When github-formatted output was introduced, workflow commands were
  automatically emitted in addition to the selected output format when the
  environment variable GITHUB_ACTIONS was true.
  • Special output format for Github actions #1599
  • fix Special output format for Github actions #1599 #1785
• That behavior caused a number of problems and was reverted.
  • Invalid output when executed inside github worker #2392
  • asukaminato0721@5c27c1b6

Proposals:

1. Add a new output format (maybe full-github?) that emits both github and
   full-text outputs.
2. Allow arbitrary combinations of output formats.
3. make --[no-]-github-workflow-commands a separate option, orthogonal to --output-format

Of these, I think 1 would be the better choice? 2 seems like it creates a lot of
new "test surface" and its not clear what other use cases might be relevant.

[grievejia]

Makes sense. I think the simplest path is indeed a new full-text-with-github output format that emits both — just one new enum variant that calls both writers. Then we update action.yml to use it.

Open to other naming suggestions or alternative approaches if anyone feels strongly.

[yangdanny97]

What if we just allow users to pass the --output-format argument multiple times?

[grievejia]

@yangdanny97 That also works but feels like a bigger hammer than needed for this specific case (we haven't run into other situations where allowing multiple output format is needed). I don't feel super strongly though.

[yangdanny97]

i think full-text-with-github makes sense

[paranoa233]

#claim

[github-actions]

@paranoa233 you've claimed this issue — it's now assigned to you. Thanks for picking it up! 🎉