`names2()` needs to use length dispatch if `x` is an object

[DavisVaughan]

library(rlang)

# 2 fields, but length 5
x <- clock::year_month_day(2019, 1:5)

names2(x)
#> [1] "" ""

^{Created on 2023-03-10 with reprex v2.0.2.9000}