zcash_history: Add Orchard support

[str4d]

Per this update to ZIP 221, from NU5 activation history trees will include Orchard commitment tree metadata. We need to update the zcash_history crate to include these changes. Since the leaves are now effectively a new type from NU5, it would be ideal if we could reflect this in the types of the history trees (having a V1 / pre-Orchard tree type, and a V2 / post-Orchard tree type). At the zcashd FFI layer we would then instantiate the correct type based on some enum passed across.