JSON-RPC: some properties could be part of the schema/types instead of integers

[adbenitez]

currently there are some properties left as their low-level C-FFI type integer, instead, as recently done with chat-type, it should be a dedicated enum type so it is part of the openRPC schema file and can be auto-generated instead of manually taking from deltachat.h file

• Message.state
• chatlist flags should instead be boolean parameters to get_chatlist_entries
• contact search flags should instead be boolean parameters to get_contact_ids