refactor: organise TypeScript config and migrate helpers (#44747)

* feat: allow more 1000 steps to be created at once

* refactor: start migrating to typescript

* refactor: delete-step to ts

* refactor: migrated some helpers

* refactor: migrate create-empty-steps

* refactor: migrate create-step-between

* refactor: finish migrating to TS

* refactor: migrate tests

* fix: ensure mock.restore is done after each test

* fix: prevent double-tscing

* fix: repair the tests

* chore: use ts-node for scripts

We don't need the performance boost of incremental compilation and
ts-node is easier to work with

* refactor: consolidate tsconfigs

* refactor: replace gulp

* fix: use ts-node for build-curriculum

* fix: allow ts compilation of config

* feat: create and use create:config script

* fix: add /config to eslint projects

* fix: remove gulp script

tools/challenge-helper-scripts/helpers/get-last-step-file-content.test.ts

@@ -0,0 +1,57 @@
+import mock from 'mock-fs';
+import { getLastStepFileContent } from './get-last-step-file-content';
+
+jest.mock('./get-project-path', () => {
+  return {
+    getProjectPath: jest.fn(() => 'mock-project/')
+  };
+});
+
+jest.mock('../utils', () => {
+  return {
+    getChallengeSeeds: jest.fn(() => {
+      return {
+        lorem: 'ipsum'
+      };
+    })
+  };
+});
+
+describe('getLastStepFileContent helper', () => {
+  it('should throw if last step count does not match with numbers of steps', () => {
+    mock({
+      'mock-project/': {
+        'step-001.md': 'Lorem ipsum...',
+        'step-004.md': 'Lorem ipsum...',
+        'final.md': 'Lorem ipsum...'
+      }
+    });
+
+    expect(() => {
+      getLastStepFileContent();
+    }).toThrow();
+  });
+
+  it('should return information if steps count is correct', () => {
+    mock({
+      'mock-project': {
+        'step-001.md': 'Lorem ipsum...',
+        'step-002.md': 'Lorem ipsum...',
+        'final.md': 'Lorem ipsum...'
+      }
+    });
+
+    const expected = {
+      nextStepNum: 3,
+      challengeSeeds: {
+        lorem: 'ipsum'
+      }
+    };
+
+    expect(getLastStepFileContent()).toEqual(expected);
+  });
+
+  afterEach(() => {
+    mock.restore();
+  });
+});