perf(document): index layer read paths

editor/index.ts

@@ -4,3 +4,5 @@ export { initialToolState } from "./tools";
 export { createInitialAppState, initialEditorState } from "./initial-state";
 export type { AppStore, StateListener } from "./store";
 export { createAppStore } from "./store";
+export type { DocumentReadIndex, IndexedLayerInfo } from "./document-indexes";
+export { createDocumentReadIndex, forEachLayerBackToFront, resolveIndexedLayerBounds } from "./document-indexes";