Add test for composer files autoload

[simPod]

I think this case should not fail while it currently does.

I was not sure how and whether to fix it though, so I added a reproducible test case.

[Ocramius]

LogicException: There were no symbols found, please check your configuration.

Fairly sure this needs fixing, although it's really annoying to support all the formats of classmap, autoload-files, etc.

FWIW, this has been implemented in detail in roave/better-reflection at https://github.com/Roave/BetterReflection/blob/478ed89e695cbff3ac037ccaa713cb56aee359b4/src/SourceLocator/Type/Composer/Factory/MakeLocatorForComposerJson.php#L80-L122

EDIT: that's mostly a small rant about the fact that we keep hitting these limitations because:

1. nobody is really helping bringing roave/better-reflection up to PHP 8 compat @_@
2. this roave/better-reflection thing keeps regularly popping up in this library - would remove a lot of code

[simPod]

@Ocramius so the proper solution to this would be to work on roave/better-reflection first, right?

[Ocramius]

@simPod not sure tbh - could be, just unsure about effort

[Ocramius]

Related: https://github.com/azjezz/psl/pull/311