Create quosures in tally_n()

[krlmlr]

Recent duckplyr checks that all functions used in a dplyr verb are what they pretend they are: tidyverse/duckplyr#179. This works for most cases, except for the n() created by tally_n() . This PR fixes this.

Once we agree on the implementation, I can vendor in a copy of this function into duckplyr.

[DavisVaughan]

@krlmlr do you still use this feature in duckplyr? Would switching to dplyr::n() and base::sum() work instead?

[krlmlr]

dplyr::n() and base::sum() would be fine too, yes.

[DavisVaughan]

So to be super clear, instead of expr(n()) we could put expr(dplyr::n()), and instead of expr(sum(!!wt, na.rm = TRUE)) we could put expr(base::sum(!!wt, na.rm = TRUE)), and that'd please duckplyr? That sounds much preferable to me!

[krlmlr]

Should be good now.

[DavisVaughan]

Great thanks!