[SPARK-20537][CORE] Fixing OffHeapColumnVector reallocation

## What changes were proposed in this pull request?

As #17773 revealed `OnHeapColumnVector` may copy a part of the original storage.

`OffHeapColumnVector` reallocation also copies to the new storage data up to 'elementsAppended'. This variable is only updated when using the `ColumnVector.appendX` API, while `ColumnVector.putX` is more commonly used.
This PR copies the new storage data up to the previously-allocated size in`OffHeapColumnVector`.

## How was this patch tested?

Existing test suites

Author: Kazuaki Ishizaki <ishizaki@jp.ibm.com>

Closes #17811 from kiszk/SPARK-20537.