in many places, we use a pattern like `React.createContext({} as
Editor)` when defining contexts. This causes a problem: `{}` is not
`Editor`, but you can still `useEditor` wherever you like and your code
with run with this confusing non-editor value.
This diff updates all our `createContext` calls to default to `null`,
with an explicit check and error for missing values. Now, if you
`useEditor` outside of `<Tldraw />`, you'll get a message telling you
that it can only be used within `<Tldraw />`.
### Change Type
- [x] `sdk` — Changes the tldraw SDK
- [x] `improvement` — Improving existing features
### Release Notes
`useEditor` and other context-based hooks will now throw an error when
used out-of-context, instead of returning a fake value.
5b21ad96ae