cpp-common/bt2: add C++ component class bindings

cpp-common/bt2: add C++ component class bindings

Add C++ bindings for component classes.

Similar to how C++ bindings for components work, the
`CommonComponentClass` type is implicitly constructible from the
specialized component class types, so that it's possible to pass a
`SourceComponentClass` to something expecting a `ComponentClass`, for
instance.

Get a component class' name, description or help with the methods of the
same name.

Change-Id: Ia6301f4b37f4f86036f6e09cc2aaf49d7028c6fc
Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/11803