Across evaluated lists

[mgirlich]

Fixes #660.
Translating lists from the environment could theoretically be a breaking change:

lf %>% mutate(across(a:b, list_formula))

# Before
#> SELECT list_formula(`a`) AS `a`, list_formula(`b`) AS `b`
#> FROM `df`

# After
#> SELECT
#>   `a`,
#>   `b`,
#>   LN(`a`) AS `a_1`,
#>   SUM(`a`) OVER () AS `a_2`,
#>   LN(`b`) AS `b_1`,
#>   SUM(`b`) OVER () AS `b_2`
#> FROM `df`

But this should be quite an irrelevant corner case and the new behaviour is like in dplyr.