[Wizard] fix: Access to State

[davhdavh]

🐛 Bug Report

I am really happy we got #3648 that lets us Finish a wizard with custom buttons.

But currently you still have to keep track of the number of steps manually and disabled status.

Please make DisplayPreviousButton, DisplayNextButton, OnPreviousHandlerAsync and OnNextHandlerAsync public, so that it is possible implement same behavior as the default trivially.

🤔 Expected Behavior

Easy to make custom wizard buttons

[dvoituron]

This is not currently planned, and there are no plans to change this behavior.
Sorry, but you will still need to keep track of the number of steps.

We may consider making DisplayPreviousButton and DisplayNextButton public.
However, the OnPreviousHandlerAsync and OnNextHandlerAsyn methods must remain internal to the component.