Add child-index as param to `onTap`

[LewisAlderman]

Describe the solution you'd like

A feature I'd like to implement myself is:

I would like to select one of the child inputs (of a child-index lower than the highest filled-in child-index), and slice the (whole pin's inputted) value down to that child input, as well as clear the selected child's value.

What I believe is needed:

I think providing the index of the tapped child-input as a param of onTap should suffice.

I also believe providing this param opens up a lot of possibilities for developers to self-implement a lot of features they might ask for from this library. (like i'd be doing here!)

Describe alternatives you've considered
Looked at the top alternative libraries