NodeInterface handles entity references inconsistently

Problem

$node->type and $node->uid are both entity references - even if the one is a config entity. But the methods in node interface handle both differently, e.g. we have $node->getAuthor() return the user entity and $node->getAuthorId() return the user entity id, while $node->getType() returns the type name, i.e. it's entity id.

Proposal:

• Make $node->getType() return the config entity and $node->getTypeName() the type name.
• Use that pattern for all ER