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-existing-step-nums.test.ts

@@ -0,0 +1,74 @@
+import mock from 'mock-fs';
+import { getExistingStepNums } from './get-existing-step-nums';
+
+// NOTE:
+// Use `console.log()` before mocking the filesystem or use
+// `process.stdout.write()` instead. There are issues when using `mock-fs` and
+// `require`.
+
+describe('getExistingStepNums helper', () => {
+  it('should return the number portion of the project paths', () => {
+    mock({
+      'mock-project': {
+        'step-001.md': 'Lorem ipsum...',
+        'step-002.md': 'Lorem ipsum...'
+      }
+    });
+
+    const folder = `${process.cwd()}/mock-project/`;
+    const steps = getExistingStepNums(folder);
+    const expected = [1, 2];
+
+    expect(steps).toEqual(expected);
+  });
+
+  it('should ignore text formatting and files named final.md', () => {
+    mock({
+      'mock-project': {
+        'final.md': 'Lorem ipsum...',
+        'step-001.md': 'Lorem ipsum...'
+      }
+    });
+
+    const folder = `${process.cwd()}/mock-project/`;
+    const steps = getExistingStepNums(folder);
+    const expected = [1];
+
+    expect(steps).toEqual(expected);
+  });
+
+  it('should throw if file names do not follow naming convention', () => {
+    mock({
+      'mock-project': {
+        'step-001.md': 'Lorem ipsum...',
+        'step-002.md': 'Lorem ipsum...',
+        'step002.md': 'Lorem ipsum...'
+      }
+    });
+
+    const folder = `${process.cwd()}/mock-project/`;
+
+    expect(() => {
+      getExistingStepNums(folder);
+    }).toThrow();
+  });
+
+  it('should return empty array if there are no markdown files', () => {
+    mock({
+      'mock-project': {
+        'step-001.js': 'Lorem ipsum...',
+        'step-002.css': 'Lorem ipsum...'
+      }
+    });
+
+    const folder = `${process.cwd()}/mock-project/`;
+    const steps = getExistingStepNums(folder);
+    const expected: number[] = [];
+
+    expect(steps).toEqual(expected);
+  });
+
+  afterEach(() => {
+    mock.restore();
+  });
+});