Supplying `.ptype` in combinations reduces amount of information in error messages

[lionel-]

vctrs::vec_c(1, 1, "")
#> Error in `vec_c()`:
#> ! Can't combine `..1` <double> and `..3` <character>.

vctrs::vec_c(1, 1, "", .ptype = int())
#> Error in `vec_c()`:
#> ! Can't convert <character> to <integer>.