[13.x] Collect Tax IDs in Checkout

[driesvints]

This allows a Stripe Checkout session to collect a customer's Tax ID which can be used to calculate taxes, etc.

$checkout = $user->collectTaxIds()->checkout('price_tshirt');

More info: https://stripe.com/docs/tax/checkout/tax-ids

Additionally, I've renamed the concerns trait to handle all tax things. It's unreleased yet so not a breaking change.