Fix issue where links to subclasses of abstract class (aggregate root) are not rendered correctly

[ruthst00]

Fixes #1445

The Bug: When a Spring Data REST repository is typed to an abstract JPA entity (e.g. MealRepository extends JpaRepository<Meal, Long>) and the actual instances returned at runtime are concrete subclasses (e.g. Dinner extends Meal), DefaultSelfLinkProvider was generating incorrect self-links pointing to a non-existent subclass resource path (e.g. /dinner/1) instead of the correct base-class resource path (e.g. /meals/1). This made the self-links unresolvable (404).

Root Cause: DefaultSelfLinkProvider.createSelfLinkFor() called entityLinks.linkToItemResource(instance.getClass(), id) using the concrete runtime type (Dinner) directly. Since no repository is registered for Dinner, EntityLinks fell back to generating a path from the class name.

The Fix (commit e4d82d24):

1. DefaultSelfLinkProvider — Added a resolveRepositoryType() method that walks up the superclass hierarchy from the concrete type to find the nearest ancestor that is the exact domain type of a registered repository. The check uses Repositories.getRepositoryInformationFor(type) and verifies the declared domain type matches exactly (distinguishing Meal from Dinner, since Repositories.hasRepositoryFor() returns true for both via hierarchy lookup). Added an optional Repositories constructor parameter.
2. RepositoryRestMvcConfiguration — Updated selfLinkProvider() bean method to inject the Repositories bean.
3. Test infrastructure — Added MealRepository and DataRest1080Tests with 4 integration tests covering: correct self-link path, resolvable self-link, subclass field serialization, and collection resource self-links.

All 4 new tests pass; the 2 pre-existing test failures (RepositoryControllerIntegrationTests, PersistentEntitySerializationTests) were confirmed to exist before this fix and are unrelated.

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