lib: add bt_get_{greatest_operative,maximal}_mip_version() functions

lib: add bt_get_{greatest_operative,maximal}_mip_version() functions

This patch adds the bt_get_greatest_operative_mip_version() and
bt_get_maximal_mip_version() functions.

The bt_get_greatest_operative_mip_version() accepts a set of component
descriptors and returns, on success, the (greatest) operative message
interchange protocol (MIP) version for all those descriptors.

bt_get_greatest_operative_mip_version() can fail if any component class's "get
supported MIP versions" fails. It can also return
`BT_GET_OPERATIVE_MIP_VERSION_STATUS_NO_MATCH` if any component
descriptor does not support MIP version 0, the only MIP version
currently supported by the the library.

bt_get_maximal_mip_version() returns the maximal MIP version supported
by the library (currently 0).

The purpose of both functions is to be used eventually to create a graph
of which all the components and the library itself operate using a
specific MIP. You can use bt_get_greatest_operative_mip_version() to find the
greatest compatible MIP version to be used by that set of component
descriptors, or you can use bt_get_maximal_mip_version() to get the
greatest MIP version possible for that library.

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Change-Id: If3875b3d76ddca2b4d58a18a829394eadb3bcd39
Reviewed-on: https://review.lttng.org/c/babeltrace/+/1872
Tested-by: jenkins <jenkins@lttng.org>
Reviewed-by: Simon Marchi <simon.marchi@efficios.com>