arrow

ARROW-15173: [R] Provide backward compatibility for bridge to older versions of pyarrow

This PR updates the pointer logic that changed in #12011 (ARROW-15169) to make sure that users can use the arrow R package to communicate with pyarrow that hasn't been upgraded yet.

Should work with:

``` bash
pip3 install pyarrow
```

``` r
pa <- reticulate::import("pyarrow", convert = FALSE)
py <- pa$array(c(1, 2, 3))
reticulate::py_to_r(py)
#> [
#>   1,
#>   2,
#>   3
#> ]
```

and:

``` bash
pip3 install pyarrow --extra-index-url https://repo.fury.io/arrow-nightlies/ --pre --upgrade
```

``` r
pa <- reticulate::import("pyarrow", convert = FALSE)
py <- pa$array(c(1, 2, 3))
reticulate::py_to_r(py)
#> [
#>   1,
#>   2,
#>   3
#> ]
```

...but we don't have a good way to test against the old pyarrow version in our tests (unless @jonkeane can think of one!)

Closes #12062 from paleolimbot/r-bridge-compat

Authored-by: Dewey Dunnington <dewey@fishandwhistle.net>
Signed-off-by: Jonathan Keane <jkeane@gmail.com>