feat: support experimental doc entries
- Params/options/members are marked as experimental in the docs.
- `experimental.d.ts` is generated that contains all types and
includes experimental features.
- `experimental.d.ts` is references in our tests so that we
can test experimental features.
- `fonts` option is restored as experimental.
There are 3 ways to import `@playwright/test` library in the modern Node.js ecosystem:
- Using `require`: works great, this patch doesn't change it
- Using `import` statement from `.mjs` file - we have wrong `default` for @playwright/test that should be a `test`. This is what test checks for
- Using `import test from '@playwright/test'` from `.ts` file - was broken because TypeScript thought it's a CJS module, whereas it's a ESM module in reality.
Also, typescript types import from `.d.ts` file was broken because we had no default export (`export *` syntax does not export default).
