Fix invalid handling of checkouts without shipping

[orzechdev]

Changes:

• In general, make checkout working without shipping if it is not required.
• Fix Checkout for digital products #258
• Fix Invalid handling of checkouts without shipping #400
• Fix Checkout with digital product and removed physical product  #541

Notion:

• Updated graphql dependency due to Error: Cannot find module 'graphql/validation/rules/PossibleTypeExtensions' when apollo codegen:generate --target=typescript types executed.

Refactor (tldr: redirection and determination of checkout route is moved to a higher position in the components hierarchy):

• Create useCheckoutStepState() hook to handle state of step and removed step out of checkout context - it should not be there as there it is not connected with context, step state is just memoization of step, where the user left his/her work. Moreover step state now can depend on other contexts and data, so it is not tight coupled with checkout context anymore.
• Remove StepCheck out of checkout pages - the logic of redirection to prevent user from entering invalid step by manually pasting the url is moved to main index.js of checkout, i.e. CheckoutApp.
• Refactor CheckoutDispatcher and move it to routes directory as CheckoutRouteDispatcher.

Screenshots

Pull Request Checklist

1. All visible strings are translated with proper context.
2. All data-formatting is locale-aware (dates, numbers, and so on).
3. The changes are tested.
4. The code is documented (docstrings, project documentation).
5. Changes are mentioned in the changelog.

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