[bugfix] Avoid randomness at init time to allow running on cloudflare. (#3016)

Describe what your pull request does. If appropriate, add GIFs or images
showing the before and after.

Follow up to #2987 

### Change Type

- [x] `patch` — Bug fix


### Release Notes

- Prevent using randomness API at init time, to allow importing the
tldraw package in a cloudflare worker.

packages/editor/src/lib/config/TLSessionStateSnapshot.ts

@@ -50,8 +50,9 @@ function iOS() {
  * A string that is unique per browser tab
  * @public
  */
-export const TAB_ID: string =
+export const TAB_ID: string = window
-	window?.[tabIdKey] ?? window?.sessionStorage[tabIdKey] ?? `TLDRAW_INSTANCE_STATE_V1_` + uniqueId()
+	? window[tabIdKey] ?? window.sessionStorage[tabIdKey] ?? `TLDRAW_INSTANCE_STATE_V1_` + uniqueId()
+	: '<error>'
 if (window) {
 	window[tabIdKey] = TAB_ID
 	if (iOS()) {

packages/editor/src/lib/config/TLUserPreferences.ts

@@ -240,18 +240,24 @@ const channel =
 
 channel?.addEventListener('message', (e) => {
 	const data = e.data as undefined | UserChangeBroadcastMessage
-	if (data?.type === broadcastEventKey && data?.origin !== broadcastOrigin) {
+	if (data?.type === broadcastEventKey && data?.origin !== getBroadcastOrigin()) {
 		globalUserPreferences.set(migrateUserPreferences(data.data))
 	}
 })
 
-const broadcastOrigin = uniqueId()
+let _broadcastOrigin = null as null | string
+function getBroadcastOrigin() {
+	if (_broadcastOrigin === null) {
+		_broadcastOrigin = uniqueId()
+	}
+	return _broadcastOrigin
+}
 const broadcastEventKey = 'tldraw-user-preferences-change' as const
 
 function broadcastUserPreferencesChange() {
 	channel?.postMessage({
 		type: broadcastEventKey,
-		origin: broadcastOrigin,
+		origin: getBroadcastOrigin(),
 		data: {
 			user: getUserPreferences(),
 			version: userMigrations.currentVersion,