lib: add MIP 1 pre-conditions for functions taking a selector / length field class

lib: add MIP 1 pre-conditions for functions taking a selector / length field class

MIP 1 deprecates referring to selector and length fields by passing a
field class pointer.

Add pre-condition checks for all functions that accept a selector or
length field class, to verify that the graph's MIP version is 0.

Add new macros in assert-cond.h to check for MIP version equality.

Philippe updated the documentation.

Change-Id: I980d8117c7460f79cfe802e2aba90eee71bc807a
Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/7315
Tested-by: jenkins <jenkins@lttng.org>
Reviewed-by: Philippe Proulx <eeppeliteloop@gmail.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/7198