Use types from the oxidized_by_ref crate instead of the oxidized crate for to_oxidized
Summary: This diff replaces the use of the oxidized typechecker types in `to_oxidized`, replacing them with oxidized_by_ref definitions. This unblocks deleting typechecker types and decls from the oxidized crate, since they are used only in this debugging-only path. It also reduces the amount of conversion necessary for `to_oxidized` (since we need not convert the oxidized_by_ref structures the typechecker already uses, like `Ty`).
Differential Revision:
D21587518
fbshipit-source-id:
5e7ec2237d0059070653b45d15eb7c1259588ccb