derived presence state (#1204)

This PR adds

- A new `TLInstancePresence` record type, to collect info about the
presence state in a particular instance of the editor. This will
eventually be used to sync presence data instead of sending
instance-only state across the wire.
- **Record Scopes**

`RecordType` now has a `scope` property which can be one of three
things:
- `document`: the record belongs to the document and should be synced
and persisted freely. Currently: `TLDocument`, `TLPage`, `TLShape`, and
`TLAsset`
- `instance`: the record belongs to a single instance of the store and
should not be synced at all. It should not be persisted directly in most
cases, but rather compiled into a kind of 'instance configuration' to
store alongside the local document data so that when reopening the
associated document it can remember some of the previous instance state.
Currently: `TLInstance`, `TLInstancePageState`, `TLCamera`, `TLUser`,
`TLUserDocument`, `TLUserPresence`
- `presence`: the record belongs to a single instance of the store and
should not be persisted, but may be synced using the special presence
sync protocol. Currently just `TLInstancePresence`

This sets us up for the following changes, which are gonna be pretty
high-impact in terms of integrating tldraw into existing systems:

- Removing `instanceId` as a config option. Each instance gets a
randomly generated ID.
- We'd replace it with an `instanceConfig` option that has stuff like
selectedIds, camera positions, and so on. Then it's up to library users
to get and reinstate the instance config at persistence boundaries.
- Removing `userId` as config option, and removing the `TLUser` type
altogether.
- We might need to revisit when doing auth-enabled features like locking
shapes, but I suspect that will be separate.

packages/editor/setupTests.js

@@ -1,6 +1,6 @@
 require('fake-indexeddb/auto')
 global.ResizeObserver = require('resize-observer-polyfill')
-global.crypto = new (require('@peculiar/webcrypto').Crypto)()
+global.crypto ??= new (require('@peculiar/webcrypto').Crypto)()
 global.FontFace = class FontFace {
 	load() {
 		return Promise.resolve()