Graduate __experimental_woocommerce_blocks_checkout_update_order_from_request PHP action to stable.

[nerrad]

This PHP action was added a few months ago. It gives extensions the chance to update orders based on the data in the request.

Things to do:

• Introduce a new action with the experimental prefix removed.
• Deprecate the old action (so it will still fire, but have it throw a deprecated developer notice pointing to the new name.
• Update inline code documentation.
• Update any other documentation.
• Check this action off in the list