sink.ctf.fs: write bit array field classes and fields

sink.ctf.fs: write bit array field classes and fields

This patch makes a `sink.ctf.fs` component handle bit array field classes
and fields. Because CTF 1.8 has no bit array field class type, it makes a
best effort and translates it to an unsigned integer field class with
a hexadecimal base.

When a `src.ctf.fs` component reads a trace generated by `sink.ctf.fs`
where the input trace IR contained bit array field classes, the
corresponding unsigned integer field classes will stay unsigned integer
field classes; the source component has no way to determine if the
metadata describes a bit array field class or a genuine unsigned integer
field class. However, the CTF 1.8 to CTF 1.8 scenario will always be
unambiguous because a `src.ctf.fs` component never creates bit array
field classes.

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Change-Id: I6375723d8513b06f984dc27f88d3d9b668191d21
Reviewed-on: https://review.lttng.org/c/babeltrace/+/1911
Tested-by: jenkins <jenkins@lttng.org>
Reviewed-by: Francis Deslauriers <francis.deslauriers@efficios.com>