This PR restores `createTLSchema`.
It also:
- removes `TldrawEditorConfig.default`
- makes `config` a required property of `<TldrawEditor>`, though it's
created automatically in `<Tldraw>`.
- makes `config` a required property of `App`
- removes `TLShapeType` and replaces the rare usage with
`TLShape["type"]`
- adds `TLDefaultShape` for a union of our default shapes
- makes `TLShape` a union of `TLDefaultShape` and `TLUnknownShape`
### Change Type
- [x] `major` — Breaking Change
### Release Notes
- [editor] Simplifies custom shape definition
- [tldraw] Updates props for <TldrawEditor> component to require a
`TldrawEditorConfig`.
eb26964130