This PR removes the strict state checks for the brush and zoom brush. We
should consider making the canvas more controlled by what exists (e.g.
whether a `brush` exists) rather than depending on particular statechart
states.
### Change Type
- [x] `minor`
### Test Plan
1. Create a brush manually in the API.
2. The brush should be visible on the canvas.
### Release Notes
- [editor] remove `editor.isIn` state checks for displaying brush and
zoom brush.
7fe43bb2ef