Record documentation-comment reference packages in TypesInUse

[knutwannheden]

Motivation

TypesInUse deliberately excludes fully qualified documentation-comment references (Javadoc {@link com.foo.Bar}, and the equivalent constructs in the other languages that share the JavaType attribution — C# <see cref="..."/>, etc.) from its import-retention set, because such a reference needs no import and must not count toward import retention (#5738). The consequence is that ChangePackage could not rely on TypesInUse to discover those references, so it grew its own dedicated full-compilation-unit walk to rediscover them for its precondition. That duplicated the "is this a fully qualified doc reference" predicate in two places with opposite intent — FindTypesInUse to exclude, ChangePackage to recover — which is precisely the kind of drift that produced the regression fixed in #7284. It also meant an extra per-file, per-recipe-instance traversal alongside the one TypesInUse already performs and caches.

This records the packages of those excluded references once, as a byproduct of the single FindTypesInUse walk, and lets ChangePackage consume them — removing the duplicated predicate and the redundant traversal. Only the package is retained, since that is all a package-renaming recipe asks of a doc reference; this also keeps the in-memory shape aligned with the package-keyed form a future serialized precondition would use.

Examples

ChangePackage's precondition doc-reference branch collapses from its own dedicated full-tree visitor to a single lookup against the already-cached TypesInUse:

if (cu.getTypesInUse().hasDocReferenceInPackage(oldPackageName, recursive)) {
    return SearchResult.found(cu);
}

Summary

• Add a separate docReferencePackages bucket to TypesInUse, populated during FindTypesInUse with the packages of fully qualified documentation-comment references — the references that are (still) excluded from the import-retention typesInUse set.
• The import-retention set is byte-for-byte unchanged, so RemoveUnusedImports, UsesType, and the FQN trie behave exactly as before. The new bucket is consulted only by callers that explicitly want it.
• Add TypesInUse.hasDocReferenceInPackage(packageName, recursive), mirroring the per-type package check package-renaming recipes apply to typesInUse. The raw set is not exposed — the query method is the only entry point.
• Rewire ChangePackage's precondition to call it and delete its bespoke documentation-comment walk, so the fully-qualified-doc-reference predicate now lives in exactly one place.
• The bucket is transient: it is populated only by TypesInUse.build(...) and left empty by TypesInUse.of(...), since a serialized type index carries no doc references. No serialization-format change.

Test plan

• New TypesInUseTest.recordsFullyQualifiedJavadocReferencesSeparately — uses a Java {@link} fixture to verify the reference is excluded from getTypesInUse() yet its package is discoverable via hasDocReferenceInPackage, covering exact / recursive / non-matching package queries.
• ChangePackageTest (including the #2537 fully-qualified-Javadoc cases) stays green — behavior preserved.
• RemoveUnusedImportsTest stays green — the import-retention set is unchanged (Remove fully qualified JavaDoc references from TypesInUse for RemoveUnusedImports #5738 behavior intact).
• Kotlin ChangePackageTest stays green — the shared recipe behaves the same on the extended J model.