block: add partition uuid into uevent as "PARTUUID"

Both most common formats have uuid in addition to partition name:
GPT: standard uuid xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx
DOS: 4 byte disk signature and 1 byte partition xxxxxxxx-xx

Tools from util-linux use the same notation for them.

Signed-off-by: Konstantin Khlebnikov <[e-mail]>
Reviewed-by: Kyle Fortin <[e-mail]>
[dianders: rebased to modern kernels]
Signed-off-by: Douglas Anderson <[e-mail]>
Signed-off-by: Douglas Anderson <[e-mail]>
Reviewed-by: Christoph Hellwig <[e-mail]>
Link: https://lore.kernel.org/r/20241004171340.v2.1.I938c91d10e454e841fdf5d64499a8ae8514dc004@changeid
Signed-off-by: Jens Axboe <[e-mail]>

block/partitions/core.c

···
 	add_uevent_var(env, "PARTN=%u", bdev_partno(part));
 	if (part->bd_meta_info && part->bd_meta_info->volname[0])
 		add_uevent_var(env, "PARTNAME=%s", part->bd_meta_info->volname);
+	if (part->bd_meta_info && part->bd_meta_info->uuid[0])
+		add_uevent_var(env, "PARTUUID=%s", part->bd_meta_info->uuid);
 	return 0;
 }