src.text.pretty: handle BLOB fields

src.text.pretty: handle BLOB fields

Make the `src.text.pretty` components handle BLOB fields, by naively
printing all bytes in hex (without a 0x prefix).  Example output:

    da-ec-name: { blob_without_len = { 23 69 6e 63 6c 75 64 65 20 3c } }

It would be nice to limit the number of bytes dumped (and provide an
option to control it), because at some point it's useless for the user
to dump thousands of bytes on one line.  But this is enough to say that
the `src.text.pretty` component class supports BLOB field classes (and
MIP 1).

Change-Id: Ia83e6429336d71082c35aa11153c9646e98e9bce
Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/7581
Tested-by: jenkins <jenkins@lttng.org>
Reviewed-by: Philippe Proulx <eeppeliteloop@gmail.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/7574