Add C++ interface for the libbabeltrace2 `bt_integer_range_*` API

Add C++ interface for the libbabeltrace2 `bt_integer_range_*` API

This patch adds C++ wrappers for Babeltrace 2 integer range objects.

The two new available types are `bt2::ConstUnsignedIntegerRange` and
`bt2::ConstSignedIntegerRange`.

Get the lower and upper bounds of an integer range object with its
lower() and upper() methods.

Compare compatible integer ranges with with operator==() and
operator!=().

You can't create such objects: they are what integer range set methods
(not part of `src/cpp-common/bt2` yet) return.

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Change-Id: I712a34756aa170b862b358e3553814ffa59547e8
Reviewed-on: https://review.lttng.org/c/babeltrace/+/4597