#14522650 A4A: Show referral order confirmation message.

Closes Automattic/jetpack-genesis#343

Proposed Changes

• Add Official A4A banner layout component. This is necessary to ensure consistent spacing. We will need to update any existing notifications to use the official banner layout on a separate PR.
• Add a new hook to simplify URL query param usage that ties with UI state. This is a recurring pattern, and we need to simplify this implementation for later usage.
• Implement the NewReferralOrderNotification component using the A4A banner layout, which will be rendered when the referral email URL query parameter is present.
• Update the Checkout flow for the Referral purchases to redirect user with Referral email in the URL parameter.

Testing Instructions

• Use the A4A live link and go to /marketplace/products

• Enable ‘Referral` mode.

• Add a few items to the cart, then proceed to checkout.
  

• On the checkout page, input a referral email and request payment.
  

• Confirm that you are redirected to the Referrals dashboard with the Order confirmation.
  

Pre-merge Checklist

• Has the general commit checklist been followed? (PCYsg-hS-p2)
• Have you written new tests for your changes?
• Have you tested the feature in Simple (P9HQHe-k8-p2), Atomic (P9HQHe-jW-p2), and self-hosted Jetpack sites (PCYsg-g6b-p2)?
• Have you checked for TypeScript, React or other console errors?
• Have you used memoizing on expensive computations? More info in Memoizing with create-selector and Using memoizing selectors and Our Approach to Data
• Have we added the “[Status] String Freeze” label as soon as any new strings were ready for translation (p4TIVU-5Jq-p2)?
• For changes affecting Jetpack: Have we added the “[Status] Needs Privacy Updates” label if this pull request changes what data or activity we track or use (p4TIVU-aUh-p2)?