This PR adds a component for `ShapeIndicators` to the UI component
overrides. It moves the "select tool" state logic up to the new
`TldrawShapeIndicators` component.
### Change type
- [ ] `bugfix`
- [x] `improvement`
- [ ] `feature`
- [x] `api`
- [ ] `other`
### Release notes
- Added new `ShapeIndicators` component to `components` object.
- Added new `TldrawShapeIndicators` component.