[EuiStepHorizontal] needs to extend HTMLButtonElement types

[thompsongl]

#4135 changed the base element of EuiStepHorizontal from a div to a button, but the base element types were removed rather than converted.

Need to reinstate the type extensions with the correct element.

[myasonik]

Oops, sorry!

Is there a good explainer for when a component needs to extend a base HTML element type and when it doesn't?

[thompsongl]

Not a problem! I approved it 😅

General rule: if the component props get spread ({...rest}) onto a HTML element, the component should extend the types of said HTML element. In this case, we just need to use ButtonHTMLAttributes<HTMLButtonElement> where HTMLAttributes<HTMLDivElement> was previously.