This PR adds a custom tool example, the `Screenshot Tool`.
It demonstrates how a user can create a custom tool together with custom
tool UI.
### Change Type
- [x] `minor` — New feature
### Test Plan
1. Use the screenshot example
### Release Notes
- adds ScreenshotTool custom tool example
- improvements and new exports related to copying and exporting images /
files
- loosens up types around icons and translations
- moving `StateNode.isActive` into an atom
- adding `Editor.path`
14e8d19a71