RESTEasy Links provider should use correct class loader

Links provider uses `Class.forName` method (https://github.com/resteasy/Resteasy/blob/4.5.2.Final/resteasy-links/src/main/java/org/jboss/resteasy/links/impl/AbstractLinksProvider.java#L84) to get a response class to be used for link resolution. This works in a usual scenario, but it fails with Quarkus dev mode. It must be because of a different class loaders used in this mode.

Using a specific entity class loader fixes the issue.