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/constants.ts

@@ -0,0 +1,15 @@
+export const DRAGGING_THRESHOLD = 10; // 10px
+export const ELEMENT_SHIFT_TRANSLATE_AMOUNT = 5;
+export const ELEMENT_TRANSLATE_AMOUNT = 1;
+export const TEXT_TO_CENTER_SNAP_THRESHOLD = 30;
+export const CURSOR_TYPE = {
+  TEXT: "text",
+  CROSSHAIR: "crosshair",
+  GRABBING: "grabbing",
+};
+export const POINTER_BUTTON = {
+  MAIN: 0,
+  WHEEL: 1,
+  SECONDARY: 2,
+  TOUCH: -1,
+};