[R] Export functions for low-level pointer operations

### Describe the enhancement requested

It would be useful to have exported the following functions used when using the Arrow C interface.

https://github.com/apache/arrow/blob/2e8bd8d0b53560a561656337021abc3e4aa73f8c/r/R/python.R#L18-L32

- allocate_arrow_schema
- delete_arrow_schema
- allocate_arrow_array
- delete_arrow_array
- allocate_arrow_array_stream
- delete_arrow_array_stream

For now, these could easily be solved by having a dependency on `nanoarrow`, as it appears that the equivalent functions are provided by `nanoarrow`, but given that the functions already exist in `arrow`, it is not clear that it would be worthwhile for the `arrow` package not to export them.

### Component(s)

R