For Doctrine ORM 2.8 we should add a metadata driver using Attributes, based off the AnnotationDriver with some adjustment to account for the missing nested support.

Idea:

• Re-use Doctrine\ORM\Mapping\* annotation classes and add #[Attribute] as needed.
• Flatten @JoinTable by introducing new InverseJoinColumn attribute
• Flatten @Table by allowing Index and UniqueConstraint on the entity/class level.
• Drop support for named queries and named native queries in Attribute based mapping driver due to their nesting complexity.
• No support for association overrides in Attribute based mapping driver.