Report files checked

[abitrolly]

Unfortunately shellcheck doesn't report files being checked - koalaman/shellcheck#2228

And reviewdog also doesn't report mistakes - pkgxdev/setup#259

So it is not clear if it is reviewdog or shellcheck failing, but if there was shellcheck reporting to console, at least one part could be more clear.

[shogo82148]

This is the intended behavior.
Reviewdog reports only the issues found in the changes made within the Pull Request.
If there are differences in the Pull Request, it will display the issues as shown in the link below:

• https://github.com/shogo82148/pkgx-setup/pull/1/files

[abitrolly]

So it is a technical limitation that it it impossible to comment on lines that are not changed, right?

In that case it still would be nice for reviewdog to report which files were detected (and they were detected, because they have changes) and which shellcheck lines it was able (and not able) to report.

So...

1. List all files (and say that these are only changed ones)
2. Get all shellchecks
3. List all shellchecks that are reported
4. List shellchecks that were left out for now, maybe with a diff/patch to be applied manually