condition: implement lttng_condition_event_rule_get_internal_capture_descriptor_at_index

condition: implement lttng_condition_event_rule_get_internal_capture_descriptor_at_index

The lttng_capture_descriptor object is only exposed internally. A
getter is necessary to allow more control on the
lttng_capture_descriptor object. This will be reused to set the bytecode
later in the patchset.

Signed-off-by: Jonathan Rajotte <jonathan.rajotte-julien@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Change-Id: I7fdfdc9d2ac1920bcf1a098352dfd105949e1062
Depends-on: lttng-ust: I5a800fc92e588c2a6a0e26282b0ad5f31c044479