Support treating any non-internal (non-test) class as part of the public API

[stof]

Many packages don't use @api at all. Instead, anything that is not tagged as @internal is considered part of the public API (this of course excludes test code which is not shipped as part of the public package).

It would be great to have a configuration setting to change how Psalm defines the public API, to make it usable in such packages. My current approach is that I have to identify issue handlers that I need to suppress because the rules rely on the definition of the public API, which is fragile and also suppresses those errors for internal classes.

[psalm-github-bot[bot]]

Hey @stof, can you reproduce the issue on https://psalm.dev? These will be used as phpunit tests when implementing the feature or fixing this bug.