This PR adds support for multiple scribbles at the same time. It
prevents the sudden disappearance of existing scribbles when new ones
are added. It simplifies the management of scribbles by moving the
scribble manager to the editor.
### Change Type
- [x] `minor` — New feature
### Test Plan
1. Use the eraser, scribble select, and laser pointer tools
- [x] Unit Tests
### Release Notes
- [feature] multi scribbles
19645b771d