Make all operations on elements array immutable (#283)

* Make scene functions return array instead of mutate array

- Not all functions were changes; so the given argument was a new array to some

* Make data restoration functions immutable

- Make mutations in App component

* Make history actions immutable

* Fix an issue in change property that was causing elements to be removed

* mark elements params as readonly & remove unnecessary copying

* Make `clearSelection` return a new array

* Perform Id comparisons instead of reference comparisons in onDoubleClick

* Allow deselecting items with SHIFT key

- Refactor hit detection code

* Fix a bug in element selection and revert drag functionality

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

src/scene/scrollbars.ts

@@ -7,7 +7,7 @@ export const SCROLLBAR_WIDTH = 6;
 export const SCROLLBAR_COLOR = "rgba(0,0,0,0.3)";
 
 export function getScrollBars(
-  elements: ExcalidrawElement[],
+  elements: readonly ExcalidrawElement[],
   canvasWidth: number,
   canvasHeight: number,
   scrollX: number,
@@ -76,7 +76,7 @@ export function getScrollBars(
 }
 
 export function isOverScrollBars(
-  elements: ExcalidrawElement[],
+  elements: readonly ExcalidrawElement[],
   x: number,
   y: number,
   canvasWidth: number,