src.ctf.fs: make ctf_fs_trace's logger private

src.ctf.fs: make ctf_fs_trace's logger private

Rename `ctf_fs_trace::logger` to `ctf_fs_trace::_mLogger` and make
private.  Pass a logger down to some functions that would previously get
it from the trace.

Change-Id: Ieae140125ac14595845739534d6bb0ee65ae114d
Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/8372
Reviewed-by: Philippe Proulx <eeppeliteloop@gmail.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/12745