So we were kinda bending over backwards to capture the use case where we
update the arrow's terminal x,y coords when unbinding, copy-pasting, and
duplicating.
- At first we abused the `onBeforeShapeDelete` callbacks, but that was
footgunny.
- Then we created a `onBeforeUnbind` callback, which was less footgunny
but still subtly footgunny.
This PR proposes reverting the `onBeforeUnbind` stuff, taking us back to
having `onBeforeShapeDelete` stuff. But at the same time it adds
`onBeforeShapeIsolate` callbacks which are triggered at the following
times:
- When you delete the other shape in a bound shape pair
- When you copy/paste or duplicate one shape in a bound shape pair but
not the other one
- When you opt-in while deleting bindings e.g. `deleteBindings([...],
{isolateShapes: true})`
This PR also fixes the bound arrow drag interaction. We can probably
extract that out to a separate PR if needed.
### Change Type
<!-- ❗ Please select a 'Scope' label ❗️ -->
- [x] `sdk` — Changes the tldraw SDK
- [ ] `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 ❗️ -->
- [x] `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. Add a step-by-step description of how to test your PR here.
2.
- [ ] Unit Tests
- [ ] End to end tests
### Release Notes
- Add a brief release note for your PR here.
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