rename app folder to editor (#1528)

Turns out there was one last terrible renaming PR to make. This PR
renames the `@tldraw.editor`'s `app` folder to `editor`. It should not
effect exports but it will be a gnarly diff.

### Change Type

- [x] `internal` — Any other changes that don't affect the published
package (will not publish a new version)

packages/editor/src/lib/config/createTLStore.ts

@@ -1,6 +1,6 @@
 import { Migrations, Store, StoreSnapshot } from '@tldraw/store'
 import { TLRecord, TLStore, createTLSchema } from '@tldraw/tlschema'
-import { TLShapeUtilConstructor } from '../app/shapeutils/ShapeUtil'
+import { TLShapeUtilConstructor } from '../editor/shapeutils/ShapeUtil'
 
 /** @public */
 export type TLShapeInfo = {