src/cpp-common: add bt2_common::{little,big}ToNative()

src/cpp-common: add bt2_common::{little,big}ToNative()

Those are C++ versions (using overloads) of the {le,be}{16,32,64}toh()
functions found in `src/compat/endian.h`.

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Change-Id: Iab826bb633388d5ce506b4462b7a0417c2c05ad4
Reviewed-on: https://review.lttng.org/c/babeltrace/+/7927
Reviewed-by: Francis Deslauriers <francis.deslauriers@efficios.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/10814
Tested-by: jenkins <jenkins@lttng.org>