Implement CTF-IR field types getters

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

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Tests: Add an array type and field test

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