Add digits argument to tbl_hierarchical()

[edelarua]

What changes are proposed in this pull request?

• Added digits argument to tbl_hierarchical() and tbl_hierarchical_count().
• Updated statistic argument to tbl_hierarchical() and tbl_ard_hierarchical() to accept formula-list-selector type.

Also removed unused type code.

Closes #2032

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[ddsjoberg]

Everything looks great! Can we make two changes? Make the statistic and digits argument accept the list-formula notation, with defaults statistic = ~"{n} ({p})", digits = NULL (or whatever makes the most sense)

[edelarua]

@ddsjoberg this is updated now!

[ddsjoberg]

THank you @edelarua !!