Refactor (#862)

* Initial factoring out of parts of the LayerUI component

2360 → 2224 LOC

* Create a Section component

* Break up src/index.tsx

* Refactor actions to reduce duplication, fix CSS

Also consolidate icons

* Move scene/data.ts to its own directory

* Fix accidental reverts, banish further single-character variables

* ACTIVE_ELEM_COLOR → ACTIVE_ELEMENT_COLOR

* Further refactoring the icons file

* Log all errors

* Pointer Event polyfill to make the tests work

* add test hooks & fix tests

Co-authored-by: dwelle <luzar.david@gmail.com>

src/scene/index.ts

@@ -7,19 +7,9 @@ export {
   getElementsWithinSelection,
   getCommonAttributeOfSelectedElements,
   getSelectedElements,
+  getTargetElement,
 } from "./selection";
-export {
-  exportCanvas,
-  loadFromJSON,
-  loadFromBlob,
-  saveAsJSON,
-  restoreFromLocalStorage,
-  saveToLocalStorage,
-  exportToBackend,
-  importFromBackend,
-  loadScene,
-  calculateScrollCenter,
-} from "./data";
+export { normalizeScroll, calculateScrollCenter } from "./scroll";
 export {
   hasBackground,
   hasStroke,