src.ctf.fs: add GMappedFileUP

src.ctf.fs: add GMappedFileUP

Add GMappedFileUP, a unique_ptr type used to manage the lifetime of a
GMappedFile object.

Change-Id: Ibc47d3c6e052499013cb34782b112ff1e72eab46
Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/8311
Reviewed-by: Philippe Proulx <eeppeliteloop@gmail.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/10846
Tested-by: jenkins <jenkins@lttng.org>
CI-Build: Philippe Proulx <eeppeliteloop@gmail.com>