field-class.hpp: Add CommonBaseEnumerationFieldClass

field-class.hpp: Add CommonBaseEnumerationFieldClass

This is useful to call the `size()` method without knowing if the
enumeration field class is of the signed or unsigned type.

Signed-off-by: Francis Deslauriers <francis.deslauriers@efficios.com>
Change-Id: I952fc54c015f8548489aab74e85cded23f9841f7
Reviewed-on: https://review.lttng.org/c/babeltrace/+/7510
Reviewed-by: Philippe Proulx <eeppeliteloop@gmail.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/10760
CI-Build: Philippe Proulx <eeppeliteloop@gmail.com>
Tested-by: jenkins <jenkins@lttng.org>
CI-Build: Simon Marchi <simon.marchi@efficios.com>