MINOR: [C++] Add missing docstrings for ChunkedArray methods
MINOR: [C++] Add missing docstrings for ChunkedArray methods

Add a few missing docstrings for public ChunkedArray methods.

Closes #11902 from Jedi18/minor_missing_comments

Authored-by: Jedi18 <a1198ba11e2e509069427446912291167a9b1c61@gmail.com>
Signed-off-by: Antoine Pitrou <9359a4d812173b65a3a0094cd86363e79731a3c2@python.org>

kou/arrow,laurentgo/arrow,wesm/arrow,icexelloss/arrow,icexelloss/arrow,laurentgo/arrow,wesm/arrow,laurentgo/arrow,icexelloss/arrow,laurentgo/arrow,laurentgo/arrow,apache/arrow,icexelloss/arrow,kou/arrow,apache/arrow,laurentgo/arrow,apache/arrow,laurentgo/arrow,apache/arrow,kou/arrow,kou/arrow,icexelloss/arrow,icexelloss/arrow,wesm/arrow,apache/arrow,wesm/arrow,apache/arrow,laurentgo/arrow,icexelloss/arrow,laurentgo/arrow,kou/arrow,laurentgo/arrow,wesm/arrow,apache/arrow,kou/arrow,icexelloss/arrow,kou/arrow,wesm/arrow,wesm/arrow,wesm/arrow,laurentgo/arrow,laurentgo/arrow,kou/arrow,kou/arrow,apache/arrow,laurentgo/arrow,apache/arrow,apache/arrow,icexelloss/arrow,apache/arrow,kou/arrow,kou/arrow,wesm/arrow,apache/arrow,wesm/arrow,icexelloss/arrow,laurentgo/arrow,kou/arrow,laurentgo/arrow,wesm/arrow,wesm/arrow,wesm/arrow,kou/arrow,kou/arrow,apache/arrow,apache/arrow,icexelloss/arrow,wesm/arrow,icexelloss/arrow,icexelloss/arrow,icexelloss/arrow