Have the crypto crate handle some subset of state events

[BillCarsonFr]

Problem

Currently the crypto crate is not handling any state events (only handling to_device and otk, fallbacks..)
As a consequence users of the SDK must on their side do several things like

• Handling and storing the encryption state of rooms
• Managing membership (traking users, passing the correct list of devices to the olmMachine when sending events)

There can be some good amount of logic there, that different client could handle badly, like protection regarding encryption state resets, encrypt to invited members, tracking and downloading user keys...

It would make sense that the crypto SDK handles it completely.

List of events that could be handled:

• m.room.encryption
• m.room.member
• m.room.history_visibility

[poljar]

Some of it was added in #3042 and #1460.

I think we should add more specific issues if/when the need arises to store more.

Closing this now.