The problem happened because we cleared the `readonlyUrl` from shared
state. This was happening every time the url changed (so panning,
zooming,...). Now, instead of clearing the `readonlyUrl` we pull out the
room prefix and slug from the readonly url.
### Change Type
<!-- ❗ Please select a 'Scope' label ❗️ -->
- [ ] `sdk` — Changes the tldraw SDK
- [x] `dotcom` — Changes the tldraw.com web app
- [ ] `docs` — Changes to the documentation, examples, or templates.
- [ ] `vs code` — Changes to the vscode plugin
- [ ] `internal` — Does not affect user-facing stuff
<!-- ❗ Please select a 'Type' label ❗️ -->
- [ ] `bugfix` — Bug fix
- [ ] `feature` — New feature
- [x] `improvement` — Improving existing features
- [ ] `chore` — Updating dependencies, other boring stuff
- [ ] `galaxy brain` — Architectural changes
- [ ] `tests` — Changes to any test code
- [ ] `tools` — Changes to infrastructure, CI, internal scripts,
debugging tools, etc.
- [ ] `dunno` — I don't know
### Test Plan
1. Create a shared room.
2. Move the camera around.
3. We should not be constantly fetching the readonly slug.
- [ ] Unit Tests
- [ ] End to end tests
### Release Notes
- Fix an issue where readonly slug was being fetched every time the url
changed (panning, zooming,...).
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Co-authored-by: Mime Čuvalo <mimecuvalo@gmail.com>
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