ARROW-17737: [R] Groups before conversion to a Table must not be restored after collect()

[eitsupi]

If a grouped data.frame is converted to arrow dplyr query and then back to a data.frame again, the data.frame-era groups are restored, even if it is ungrouped in the query.

mtcars |>
  dplyr::group_by(cyl) |>
  arrow::arrow_table() |>
  dplyr::group_by() |>
  dplyr::ungroup() |>
  dplyr::collect() |>
  dplyr::group_vars()
#> [1] "cyl"

This PR will update to ensure that the arrow dplyr query's groups are applied when compute or collect.

[github-actions]

https://issues.apache.org/jira/browse/ARROW-17737

[eitsupi]

This is because manipulating metadata for a table with no rows will cause the size to be updated to 0 x 0.

mtcars |> arrow::arrow_table() |> dplyr::select(NULL) |> arrow::as_arrow_table()
#> Table
#> 32 rows x 0 columns
#>
#>
#> See $metadata for additional Schema metadata
mtcars |> arrow::arrow_table() |> dplyr::select(NULL) |> arrow::as_arrow_table() |> dplyr::ungroup()
#> Table
#> 0 rows x 0 columns
#>
#>
#> See $metadata for additional Schema metadata

^{Created on 2022-10-07 with reprex v2.0.2}

I don't know if this (handling of tables with no rows) is a problem.
A table with 0 rows and multiple columns appears to be quite exceptional, since creating a table from a data frame with no rows results in 0 x 0.

mtcars |> dplyr::select(NULL) |> arrow::arrow_table()
#> Table
#> 0 rows x 0 columns
#>
#>
#> See $metadata for additional Schema metadata

^{Created on 2022-10-07 with reprex v2.0.2}

[nealrichardson]

One suggestion for simplifying this change. Thanks for taking this on, will be nice to get this in the upcoming release along with your other changes around here.

[ursabot]

Benchmark runs are scheduled for baseline = d1a8f4b and contender = d008c17. d008c17 is a master commit associated with this PR. Results will be available as each benchmark for each run completes.
Conbench compare runs links:
[Finished ⬇️0.0% ⬆️0.0%] ec2-t3-xlarge-us-east-2
[Failed ⬇️1.11% ⬆️0.0%] test-mac-arm
[Failed ⬇️0.0% ⬆️0.0%] ursa-i9-9960x
[Finished ⬇️0.18% ⬆️0.0%] ursa-thinkcentre-m75q
Buildkite builds:
[Finished] d008c17e ec2-t3-xlarge-us-east-2
[Failed] d008c17e test-mac-arm
[Failed] d008c17e ursa-i9-9960x
[Finished] d008c17e ursa-thinkcentre-m75q
[Finished] d1a8f4ba ec2-t3-xlarge-us-east-2
[Failed] d1a8f4ba test-mac-arm
[Failed] d1a8f4ba ursa-i9-9960x
[Finished] d1a8f4ba ursa-thinkcentre-m75q
Supported benchmarks:
ec2-t3-xlarge-us-east-2: Supported benchmark langs: Python, R. Runs only benchmarks with cloud = True
test-mac-arm: Supported benchmark langs: C++, Python, R
ursa-i9-9960x: Supported benchmark langs: Python, R, JavaScript
ursa-thinkcentre-m75q: Supported benchmark langs: C++, Java

[ursabot]

['Python', 'R'] benchmarks have high level of regressions.
test-mac-arm