list_c() needs to deal with names

[hadley]

purrr:::list_c(list(a = 1:2, b = 1:3))
#> Error in `list_unchop()`:
#> ! Can't merge the outer name `a` with a vector of length > 1.
#> Please supply a `.name_spec` specification.

#> Backtrace:
#>     ▆
#>  1. ├─purrr:::list_c(list(a = 1:2, b = 1:3))
#>  2. │ └─vctrs::list_unchop(x, ptype = ptype, error_call = current_env())
#>  3. └─rlang::abort(message = message)

^{Created on 2022-11-05 with reprex v2.0.2}

[olivroy]

Cf from #1064 (comment), could list_c() gain name_spec instead, or a better solution exists.