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/utils/api-report.md

@@ -37,6 +37,13 @@ export type ErrorResult<E> = {
 // @internal (undocumented)
 export function exhaustiveSwitchError(value: never, property?: string): never;
 
+// @internal
+export function filterEntries<Key extends string, Value>(object: {
+    [K in Key]: Value;
+}, predicate: (key: Key, value: Value) => boolean): {
+    [K in Key]: Value;
+};
+
 // @internal (undocumented)
 export function getErrorAnnotations(error: Error): ErrorAnnotations;
 

packages/utils/src/index.ts

@@ -16,6 +16,7 @@ export { getFirstFromIterable } from './lib/iterable'
 export { lerp, modulate, rng } from './lib/number'
 export {
 	deepCopy,
+	filterEntries,
 	getOwnProperty,
 	hasOwnProperty,
 	objectMapEntries,

packages/utils/src/lib/object.ts

@@ -87,3 +87,24 @@ export function objectMapEntries<Key extends string, Value>(object: {
 }): Array<[Key, Value]> {
 	return Object.entries(object) as [Key, Value][]
 }
+
+/**
+ * Filters an object using a predicate function.
+ * @returns a new object with only the entries that pass the predicate
+ * @internal
+ */
+export function filterEntries<Key extends string, Value>(
+	object: { [K in Key]: Value },
+	predicate: (key: Key, value: Value) => boolean
+): { [K in Key]: Value } {
+	const result: { [K in Key]?: Value } = {}
+	let didChange = false
+	for (const [key, value] of objectMapEntries(object)) {
+		if (predicate(key, value)) {
+			result[key] = value
+		} else {
+			didChange = true
+		}
+	}
+	return didChange ? (result as { [K in Key]: Value }) : object
+}