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GH-29642: [R] Support for .keep_all = TRUE with distinct() (#44652)

### Rationale for this change

Support a missing feature, just wiring up some stuff from R to Acero,
then adding docs and tests.

This is mostly picking up where #13934 started and finishing it out.
Thanks @mopcup for the initial lift.

### What changes are included in this PR?

An aggregation binding, some symbol manipulation, and tests. I also
cleaned up some dplyr test shims from 2022.

### Are these changes tested?

Yes, though if anyone knows of odd corners in `distinct()` that aren't
covered by this, we can add more

### Are there any user-facing changes?

Yes indeed.
* GitHub Issue: #29642