feat(Step): add CurrentStepIndex property

[momijijin]

Is there an existing issue for this?

• I have searched the existing issues

Is your feature request related to a problem? Please describe the problem.

I want to obtain the real-time value of _currentStepIndex independently of the Prev() and Next() methods, adding 'CurrentStepIndex' instead of modifying 'StepIndex' to prevent the occurrence of destructive updates.

Describe the solution you'd like

No response

Additional context

No response

[bb-auto]

@momijijin Thank you for contacting us. We will give feedback later.