Consider updating `if_else()`

[hadley]

It's taking us longer to get to funs than expected, so it might be useful to update our if_else() to use vctrs in the meantime. This would avoid:

dplyr::if_else(TRUE, NA, 1)
#> Error in `dplyr::if_else()`:
#> ! `false` must be a logical vector, not a double vector.

^{Created on 2022-04-26 by the reprex package (v2.0.1)}