bt2: `TraceCollectionMessageIterator`: find greatest MIP version

bt2: `TraceCollectionMessageIterator`: find greatest MIP version

This patch makes the `TraceCollectionMessageIterator` object use
bt2.get_greatest_operative_mip_version() to find the greatest operative
MIP version of all the components to create, including the stream
intersection `flt.utils.trimmer` components, and then use the result to
create the graph with bt2.Graph().

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Change-Id: Id9024a2343d0e99384ae62bd77754912a4267dac
Reviewed-on: https://review.lttng.org/c/babeltrace/+/1881
Tested-by: jenkins <jenkins@lttng.org>
Reviewed-by: Simon Marchi <simon.marchi@efficios.com>