[Python][R][Docs] Update the "Integrating PyArrow with R" documentation section to not use `_import_from_c`/`_export_to_c`

Currently, the "Integrating PyArrow with R" page (https://arrow.apache.org/docs/13.0/python/integration/python_r.html) has a section on using the C Data Interface to communicate data between R and Python. This section uses the low-level `_import_from_c` / `_export_to_c` methods, and we should see if we can and should update this to not use those methods directly.