refactor: move elementLocked to activeTool.locked (#4983)

* refactor: move elementLocked to activeTool.locked

* fix

* fix snap

* update docs

* Update src/packages/excalidraw/CHANGELOG.md

* revert

* make lastActiveToolBeforeEraser required and nullable

* fix snap

src/tests/packages/__snapshots__/utils.test.ts.snap

@@ -3,6 +3,8 @@
 exports[`exportToSvg with default arguments 1`] = `
 Object {
   "activeTool": Object {
+    "lastActiveToolBeforeEraser": null,
+    "locked": false,
     "type": "selection",
   },
   "collaborators": Map {},
@@ -26,7 +28,6 @@ Object {
   "editingElement": null,
   "editingGroupId": null,
   "editingLinearElement": null,
-  "elementLocked": false,
   "errorMessage": null,
   "exportBackground": true,
   "exportEmbedScene": false,