arrow

ARROW-14989: [R] Update num_rows methods to output doubles not integers to prevent integer overflow

This PR enables `num_rows()` methods to be called on `Table` and `RecordBatch` objects without integer overflow when the value of `num_rows()` is higher than `.Machine$integer.max`.  I originally wrote some tests but they take ages to run and crashed on CI anyway so I removed them, but they can be seen in https://github.com/apache/arrow/pull/13482/commits/e7cf8a66beab6d1b7d85304362086b6205a31279/.

Closes #13482 from thisisnic/ARROW-14989_num_rows_double

Authored-by: Nic Crane <thisisnic@gmail.com>
Signed-off-by: Nic Crane <thisisnic@gmail.com>