fix: validate schema for refs with invalid visibility

[matt2e]

fixes #5313

[stuartwdouglas]

I think this failure is due to an existing problem in the JVM runtime with it not exporting decls used in other decls.

[stuartwdouglas]

Hopefully #5246 will fix the issue

[matt2e]

@stuartwdouglas yep great to fix the JVM issue 👍
I think schema validation should check it regardless, rather than rely on each language always producing valid schema. But also yeh theres the export realm case which can't be fixed by transitive exports as they can cross module boundaries.

[matt2e]

Blocked by #5315

[stuartwdouglas]

That other PR has issues unrelated to the visbillity, so I have broken out the changes into #5316