feat(Step): `Prev` `Next` function return step index

[ice6]

Is there an existing issue for this?

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

as title described.

Describe the solution you'd like

1. return _currentStepIndex in the Prev Next Reset method.
2. make the StepIndex return _currentStepIndex.

Additional context

No response

[bb-auto]

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