feat: enable reset in multifile editor (#43617)

* feat: dispatch resetChallenge action

* fix: copy challengeFiles instead of in-place sort

* fix: handle null updateFile payloads in redux

* refactor: reorganise region initialization

* refactor: pull code into editorDidMount

Then we can rely on the presence of the editor and monaco and don't have
litter the code with null checks.

* refactor: use better name for editable region init

* refactor: remove unused decoration

* refactor: rename forbidden region init functions

* fix: keep all challengeFiles when resetting

* refactor: remove unused decoration class

* fix: reinitialize editor on reset

* fix: stop adding multiple scroll listeners

Since the challengeFile update on each keystroke extra (unnecessary)
adding of listeners slowed the editor to a crawl.

* fix: only scroll to editor on mount

Rather than on any edit.

* refactor: remove logs and comments

* fix: rename toSortedArray and fix broken test

* fix: check for null not falsy in updateFile

* fix: only update project features when project

* fix: only reset if editor contents have changed

* feat: focus on editor after reset

utils/sort-challengefiles.test.js

@@ -0,0 +1,24 @@
+const { challengeFiles } = require('./__fixtures__/challenges');
+const { sortChallengeFiles } = require('./sort-challengefiles');
+
+describe('sort-files', () => {
+  describe('sortChallengeFiles', () => {
+    it('should return an array', () => {
+      const sorted = sortChallengeFiles(challengeFiles);
+      expect(Array.isArray(sorted)).toBe(true);
+    });
+    it('should not modify the challenges', () => {
+      const sorted = sortChallengeFiles(challengeFiles);
+      const expected = challengeFiles;
+      expect(sorted).toEqual(expect.arrayContaining(expected));
+      expect(sorted.length).toEqual(expected.length);
+    });
+
+    it('should sort the objects into html, css, jsx, js order', () => {
+      const sorted = sortChallengeFiles(challengeFiles);
+      const sortedKeys = sorted.map(({ fileKey }) => fileKey);
+      const expected = ['indexhtml', 'indexcss', 'indexjsx', 'indexjs'];
+      expect(sortedKeys).toStrictEqual(expected);
+    });
+  });
+});