[Payment Method Improvements] UX improvements to cash payment change calculator for parity with iOS

[backwardstruck]

In woocommerce/woocommerce-ios#11365, iOS implemented a change calculator for cash payment in the order form. We want to make the same UX improvements that iOS is doing in this ticket while implementing that same basic functionality:

GH issue: woocommerce/woocommerce-ios#12386

[dangermattic]

Thanks for reporting! 👍

[backwardstruck]

Blocked until the UI/UX changes can be coordinated at the same time as iOS.

[soundsokay]

Makes sense to hold off on these changes at this time 👍