Make bt_uuid_from_str() take begin/end pointers

Make bt_uuid_from_str() take begin/end pointers

Make bt_uuid_from_str() take begin/end pointers (null terminator not
required) to make it possible to call it with a string view.

What used to be bt_uuid_from_str() is now bt_uuid_from_c_str() to avoid
changing existing the logic of call sites.

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Change-Id: I4d7c0c434b71c684a90fa696c6654e4b3a5c055c
Reviewed-on: https://review.lttng.org/c/babeltrace/+/12758