cpp-common/bt2: add C++ query executor bindings

cpp-common/bt2: add C++ query executor bindings

Add C++ bindings for query executors.

Create a query executor with the `bt2::QueryExecutor::create()` static
methods (with or without query data).

Perform a query with the `bt2::QueryExecutor::query()` method.

Change-Id: I1db634dfd423b031be7577291d4de02b7fb0df5b
Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/11808
Tested-by: jenkins <jenkins@lttng.org>