bindings: cxx: new example
bindings: cxx: new example

Add a test case to C++ examples demonstrating the manipulation of
several lines held by a line_bulk object.

Signed-off-by: Bartosz Golaszewski <108de5fbc428215dc26df4468b48691526611148@gmail.com>

brgl/libgpiod,brgl/libgpiod,brgl/libgpiod,brgl/libgpiod