module lookup on behalf of automatic modules

Debugging #2749 for #2748 I was puzzled by the following:

We have a few code locations where we differentiate if we should look for **all** observable modules or only for all **named** modules.

[JLS §7](https://docs.oracle.com/javase/specs/jls/se22/html/jls-7.html) introduces automatic modules without any mention of what an auto module can read.

[JEP 261](https://openjdk.org/jeps/261) has nothing helpful in this regard.

Javadoc of [ModuleFinder.of()](https://docs.oracle.com/en/java/javase/22/docs/api/java.base/java/lang/module/ModuleFinder.html#of(java.nio.file.Path...)) defines how an auto module is identified, and what it exports, but no word on what it reads.

Finally the [Javadoc of package java.lang.module](https://docs.oracle.com/en/java/javase/22/docs/api/java.base/java/lang/module/package-summary.html) declares:
> If B is an automatic module, then A "reads" every other enumerated automatic module. (It is "as if" an automatic module has 'requires transitive' directives for every other enumerated automatic module).

In previous bugs like [bug 518282](https://bugs.eclipse.org/bugs/show_bug.cgi?id=518282) we worked from a version that said
> For each enumerated module X that is automatic: X "reads" every other enumerated module

where no restriction to automatic modules was present. I have no record of what "specification" we worked from in those days. I only vividly recall that we had a tremendously hard time to gather any sufficient set of specifications.

At the same time we might want to check for similar loose ends regarding the unnamed module.