feat: allow for main.ts or any other file extension

[dannyhw]

Issue: #390

What I did

Added logic to allow any file extension for main.

How to test

run the stories loader script for a project with main.ts

[diginikkari]

I think this should also be tested using very common `default export' format. Not only extension change.:

import type { StorybookConfig } from '@storybook/core-common';

const config: StorybookConfig = {
  stories: ['./FakeStory.stories.tsx'],
  addons: [
    '@storybook/addon-ondevice-notes',
    '@storybook/addon-ondevice-controls',
    '@storybook/addon-ondevice-backgrounds',
    '@storybook/addon-ondevice-actions',
  ],
};

export default config;

[dannyhw]

@diginikkari test case added and a fix for default exports.

[diginikkari]

@dannyhw looks good 👍 Now with the watcher changes this should help working with typescript 😀.
I'm so happy how RN Storybook is getting closer to current storybook. When having used to develop components in isolation with web it's so nice to be able to do it also with RN.

[dannyhw]

@diginikkari thats really great to hear, thanks :).

We have some cool plans for react native in future too 😄

[diginikkari]

We have some cool plans for react native in future too 😄

oh, looking forward to those 👀