Arc - resource provider SPI

[mkouba]

The PR should be ready now. I'll add some more description and comments tomorrow.

[mkouba]

Ok, so this is not a high priority issue but I'd like to have it merged. What's changed?

• Arc has a simple SPI ResourceReferenceProvider which makes it possible to resolve non-CDI field injection points, such as Java EE resources; it does iterate over all service providers for each field which is annotated with a resource annotation added via BeanProcessor.Builder.addResourceAnnotations()
• HibernateCdiResourceProcessor
  • registers PersistenceContext and PersistenceUnit as resource annotations and JPAResourceReferenceProvider; thus any CDI bean can e.g. do @PersistenceContext EntityManager
  • all persistence units found are bootstrapped; previously only PUs for which a CDI producer was found were registered
  • if there is no EM/EMF CDI producer found a default one is added; i.e. @Inject EntityManager works without any CDI producer defined
• There are two important CDI beans:
  • org.jboss.shamrock.jpa.runtime.JPAConfig - holds a map of bootstrapped persistence units; has @PreDestroy callback to close them
  • TransactionEntityManagers - request scoped bean that holds a map of TransactionScopedEntityManager used when JTA is enabled; has @PreDestroy callback to clean them up

When JTA is enabled for @Inject EntityManager a forwarding EntityManager is injected - this one delegates to the actual request scoped TransactionScopedEntityManager. This is not ideal but it should be fine for POC.