Return a Map of vendor-specific JPA properties for the given persistence
unit, typically based on settings in this JpaVendorAdapter instance.
Note that there might be further JPA properties defined on the
EntityManagerFactory bean, which might potentially override individual
JPA property values specified here.
This implementation delegates to getJpaPropertyMap() for
non-unit-dependent properties. Effectively, this PersistenceUnitInfo-based
variant only needs to be implemented if there is an actual need to react
to unit-specific characteristics such as the transaction type.