Button: ariaLabel prop should be required if no children are passed
Description
Add ariaLabel prop, make mandatory if there is no text in a button
aria-label is currently being spread to Buttons. We should pull this out and enforce having an aria-label for Buttons if there in no text - https://github.com/SAP/fundamental-react/blob/master/src/Button/Button.js#L82
Versions
fundamental-react: 0.13.0
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