Add `bt2::CommonArrayValueIterator` to iterate on `bt2::CommonArrayValue` container

Add `bt2::CommonArrayValueIterator` to iterate on `bt2::CommonArrayValue` container

This commit implements an array value input iterator and adds `begin()` and
`end()` methods to the `CommonArrayValue` container class.

Signed-off-by: Francis Deslauriers <francis.deslauriers@efficios.com>
Change-Id: I2e3c502bd5b11a507fc4643cee27b48b06a6c4a8
Reviewed-on: https://review.lttng.org/c/babeltrace/+/7322
Reviewed-by: Philippe Proulx <eeppeliteloop@gmail.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/7193
Tested-by: jenkins <jenkins@lttng.org>
CI-Build: Philippe Proulx <eeppeliteloop@gmail.com>