Add `bt2_common::UuidView`

Add `bt2_common::UuidView`

This patch adds the `bt2_common::UuidView` class which is like
`std::string_view`, but for UUIDs.

You cannot modify the underlying UUID (`const std::uint8_t *`).

Compare UUID views with operator==() and operator!=().

Get a UUID view's data with its data() method.

Get a UUID view's data size with its size() method.

Get the canonical string of a UUID view with its string() method, which
returns a new `std::string` instance.

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Change-Id: Icc633b44b852383d223ff8e73034736f47b64579
Reviewed-on: https://review.lttng.org/c/babeltrace/+/4601