Lectern Book Entity Should Be Part of The Block Model

Unlike on an enchanting table, the book on a lectern is completely static, so instead of using the entity model of the enchanting table book, it should be a part of the {has_book=true} lectern block model; especially considering this block state already exists for the lectern.

This would change would allow greater freedom for resource pack makers who would no longer be limited to the vanilla enchantment book entity and texture on their lecterns, which currently doesn't support transparency [MC-164001] or any kind of model changes.

Any concerns about the performance impact of this change should be convinced otherwise by the increasing complexity of newer block models such as the grindstone and campfire.