[R] Implement dplyr::across() inside group_by()

[asfimport]

Reporter: SHIMA Tatsuya / @eitsupi
Assignee: SHIMA Tatsuya / @eitsupi

Related issues:

• [R] Implement dplyr::across() inside group_by() (duplicates)
• [R] Implement dplyr::across() inside mutate() (is related to)

_{Note: This issue was originally created as ARROW-17727. Please see the migration documentation for further details.}

[asfimport]

SHIMA Tatsuya / @eitsupi:
I'm sorry, I created this without noticing ARROW-17689.