Implement CTF-IR stream getters

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Tests: Add stream getter tests

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Add Python bindings for CTF-IR stream getters

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>