* Checkout class tidyup
* CheckoutProcessor placeholder
* ShippingMethodDataX to ShippingDataX
* Remove billing from checkout provider
* Remove billing data hook
* Remove billing from payment methods state
* Update typedefs
* Billing context
* Fix billing and shipping context persistence bugs
* Remove address form change
* Move phone back; another PR can deal with this
* Remove unused state
- restructures `@woocommerce/base-context` imports so it pulls from `index.js` in the `base/context` folder. That way tree-shaking will be used if possible. This also helps with organizing the folder structure a bit better for the new contexts.
- Fixes all the various imports through the code due to the above change.
- Adds `CheckoutContextProvider`, `useCheckoutContext` and related files.
- Adds `PaymentMethodDataProvider`, `usePaymentMethodDataContext` and related files.
- Adds `ShippingMethodDataProvider`, `useShippingMethodDataContext` and related files.
- Adds typedefs used for the various context interfaces.
Mike Jolley
Darren Ethier