Rest API batching support (2)

[mikejolley]

Raising #3899 again.

When testing you must ensure you have reran npm install for the dataloader dependency.

This PR implements batching in the Store API, and a dataloader class in the client to batch requests within a certain interval.

Batching works for POST, PUT, DELETE API requests. GET requests are not affected.

As well as adding the batching, this commit creates a control to handle fragment updates and adds a timeout. This prevents multiple fragment updates after a batch of events have ran.

NOTE: I am requested feedback/code review, but some things are left to do before it can be merged:

• Check what happens if nonce changes on items in the batch.
• Batch is only supported on 5.6+ so we need the client to account for this also.
• Reduce batch timeout from 3000 - I have left this high to make testing easier.

Fixes #2094

How to test the changes in this Pull Request:

1. Go to the products page.
2. Add to items to the cart really quickly. If you focus a button with the keyboard you can hit enter and click another button.
3. Check the network request for a "batch" API call. You'll see 2 responses in an array.
4. Smoke test cart page functionality/cart/checkout. All should be unaffected.
5. Check that on the cart page, changing qty persists and the API request is successful.
6. Check that on the cart page, removing an item from the cart is successful.

Changelog

Added support to the Store API for batching requests. This allows multiple POST requests to be made at once to reduce the number of separate requests being made to the API.

[github-actions]

Size Change: +2.41 kB (0%)

Total Size: 1.16 MB

Filename	Size	Change
build/active-filters.js	8.71 kB	+3 B (0%)
build/all-products-frontend.js	35.6 kB	+1 B (0%)
build/all-products.js	36.7 kB	-254 B (-1%)
build/all-reviews.js	9.92 kB	-1 B (0%)
build/atomic-block-components/add-to-cart--atomic-block-components/button.js	1.95 kB	-262 B (-12%)	👏
build/atomic-block-components/add-to-cart--atomic-block-components/image--atomic-block-components/title.js	336 B	+1 B (0%)
build/atomic-block-components/add-to-cart-frontend.js	8.74 kB	-267 B (-3%)
build/atomic-block-components/add-to-cart.js	7.83 kB	-12 B (0%)
build/atomic-block-components/button-frontend.js	1.72 kB	-299 B (-15%)	👏
build/atomic-block-components/button.js	843 B	-53 B (-6%)	✅
build/atomic-block-components/category-list.js	476 B	-1 B (0%)
build/atomic-block-components/image-frontend.js	1.82 kB	-1 B (0%)
build/atomic-block-components/image.js	1.29 kB	-1 B (0%)
build/atomic-block-components/rating.js	525 B	+1 B (0%)
build/atomic-block-components/summary.js	926 B	+1 B (0%)
build/atomic-block-components/tag-list.js	473 B	+1 B (0%)
build/atomic-block-components/title.js	1.26 kB	-1 B (0%)
build/blocks-checkout.js	13.7 kB	+14 B (0%)
build/cart-frontend.js	77.7 kB	-13 B (0%)
build/cart.js	43.6 kB	+51 B (0%)
build/checkout-frontend.js	82 kB	+3 B (0%)
build/checkout.js	45.9 kB	+42 B (0%)
build/handpicked-products.js	6.5 kB	-1 B (0%)
build/price-filter.js	10 kB	+1 B (0%)
build/price-format.js	1.46 kB	+1 B (0%)
build/product-best-sellers.js	6.6 kB	+1 B (0%)
build/product-categories.js	3.23 kB	-1 B (0%)
build/product-on-sale.js	7.17 kB	+1 B (0%)
build/product-search.js	3.6 kB	-1 B (0%)
build/product-top-rated.js	6.73 kB	+2 B (0%)
build/reviews-by-product.js	13.5 kB	+3 B (0%)
build/single-product-frontend.js	38.7 kB	+1 B (0%)
build/single-product.js	10.3 kB	+2 B (0%)
build/vendors.js	419 kB	+19 B (0%)
build/wc-blocks-data.js	10.6 kB	+3.27 kB (+44%)	🚨
build/wc-blocks-middleware.js	1.48 kB	+160 B (+12%)	⚠️
build/wc-blocks-registry.js	2.75 kB	+2 B (0%)
build/wc-settings.js	2.83 kB	+2 B (0%)
build/wc-shared-context.js	1.54 kB	-3 B (0%)
build/wc-shared-hocs.js	1.72 kB	+4 B (0%)

ℹ️ View Unchanged

Filename	Size	Change
build/active-filters-frontend.js	8.63 kB	0 B
build/atomic-block-components/add-to-cart--atomic-block-components/button--atomic-block-components/image---a7e2bb9b.js	1.8 kB	0 B
build/atomic-block-components/category-list-frontend.js	469 B	0 B
build/atomic-block-components/price-frontend.js	1.98 kB	0 B
build/atomic-block-components/price.js	2 kB	0 B
build/atomic-block-components/rating-frontend.js	521 B	0 B
build/atomic-block-components/sale-badge-frontend.js	861 B	0 B
build/atomic-block-components/sale-badge.js	868 B	0 B
build/atomic-block-components/sku-frontend.js	391 B	0 B
build/atomic-block-components/sku.js	394 B	0 B
build/atomic-block-components/stock-indicator-frontend.js	570 B	0 B
build/atomic-block-components/stock-indicator.js	572 B	0 B
build/atomic-block-components/summary-frontend.js	918 B	0 B
build/atomic-block-components/tag-list-frontend.js	465 B	0 B
build/atomic-block-components/title-frontend.js	1.41 kB	0 B
build/attribute-filter-frontend.js	18.4 kB	0 B
build/attribute-filter.js	12.5 kB	0 B
build/blocks.js	3.49 kB	0 B
build/editor-rtl.css	14.9 kB	0 B
build/editor.css	14.9 kB	0 B
build/featured-category.js	7.87 kB	0 B
build/featured-product.js	10.1 kB	0 B
build/price-filter-frontend.js	14.8 kB	0 B
build/product-category.js	7.57 kB	0 B
build/product-new.js	6.76 kB	0 B
build/product-tag.js	6.61 kB	0 B
build/products-by-attribute.js	7.51 kB	0 B
build/reviews-by-category.js	12 kB	0 B
build/reviews-frontend.js	9.59 kB	0 B
build/style-rtl.css	18.8 kB	0 B
build/style.css	18.8 kB	0 B
build/vendors--atomic-block-components/price-frontend.js	6.54 kB	0 B
build/vendors-style-rtl.css	1.05 kB	0 B
build/vendors-style.css	1.05 kB	0 B
build/wc-blocks-google-analytics.js	1.99 kB	0 B
build/wc-payment-method-bacs.js	812 B	0 B
build/wc-payment-method-cheque.js	807 B	0 B
build/wc-payment-method-cod.js	903 B	0 B
build/wc-payment-method-paypal.js	844 B	0 B
build/wc-payment-method-stripe.js	12.3 kB	0 B

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[nerrad]

I only got a chance to do a review of the code and it looks good to me. I do have a question about removing validate_callback function in favour of an inline nonce check on the response but that is non-blocking.

If needed I can run through some testing tomorrow, but I'll pre-approve based on the code review.