* Shown express payment methods in Cart block
* Fixes
* Create usePositionRelativeToViewport hook
* Typo
* Style fixes
* Remove footer push div
* Styling fixes
* Improve code clarity
* Split ExpressCheckoutFormControl into two components
* Rename visibilityObserver to referenceElement
* Replace 'useEffect' with 'useLayoutEffect'
* Add tests for usePositionRelativeToViewport
* Self-closing div
* Add explanatory comment
* Create a shim for IntersectionObserver
* Update express payment components class names
* Add todo comment to remove IntersectionObserver shim when we drop IE11 support
Albert Juhé Lluveras