Node bindings for the matrix-sdk-crypto crate

[poljar]

A bunch of folks would really like to use the matrix-sdk-crypto crate for Javascript based projects. An initial napi based prototype was written in https://github.com/matrix-org/matrix-rust-sdk-bindings.

Those bindings lack error handling and aren't up-to-date with the latest version of the sdk. On the other hand wasm-bindgen based bindings have been started in #681.

This issue is about adopting the wasm-bindgen based bindings to also expose napi based bindings from the same codebase. The macros and types that are used by wasm-bindgen and napi are sufficiently similar that this should be relatively straightforward.

The Node bindings, at least for now, don't require the whole API surface of the matrix-sdk-crypto crate to be exposed. People are mainly interested in writing bots and bridges, thus basic encryption and decryption will be sufficient.

The methods that are needed for basic encryption/decryption are:

• OlmMachine::new()
• OlmMachine::receive_sync_changes()
• OlmMachine::outgoing_requests()
• OlmMachine::mark_request_as_sent()
• OlmMachine::decrypt_room_event()
• OlmMachine::update_tracked_users()
• OlmMachine::get_missing_sessions()
• OlmMachine::share_room_key()
• OlmMachine::encrypt_raw()

Things that are trivial to add, and nice to have, but not exactly needed:

• OlmMachine::user_id()
• OlmMachine::device_id()
• OlmMachine::identity_keys()

[poljar]

This has been closed by #721.