Add `check_has_names()`

[mgirlich]

I frequently check (in particular for data frames) that an object has certain names.
E.g. from tidyr::check_pivot_spec()

if (!has_name(spec, ".name") || !has_name(spec, ".value")) {
  cli::cli_abort(
    "{.arg spec} must have {.var .name} and {.var .value} columns.",
    call = call
  )
}