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/components/ShapeIndicator.tsx

@@ -7,8 +7,8 @@ import {
 	useValue,
 } from 'signia-react'
 import { useEditor } from '../..'
-import type { Editor } from '../app/Editor'
-import { ShapeUtil } from '../app/shapeutils/ShapeUtil'
+import type { Editor } from '../editor/Editor'
+import { ShapeUtil } from '../editor/shapeutils/ShapeUtil'
 import { useEditorComponents } from '../hooks/useEditorComponents'
 import { OptionalErrorBoundary } from './ErrorBoundary'