[orca-list] Heads-up: I've bumped the minimum versions of AT-SPI2 and ATK from 2.10 to 2.12

[Joanmarie Diggs <jdiggs igalia com>]

Hey all.

As I think most of you know, even though Orca X.y is only supported in
GNOME X.y, I try to not depend on the very latest GNOME components so
that you can use Orca master in earlier versions of your distro. But
there are a number of roles which were introduced back during GNOME 3.12
that Orca should start looking for and supporting better. I'll do that
in the weeks to come. In the meantime, it turns out that I'd already
started using one such role which was causing a traceback on a system
which had accessibility libraries from GNOME 3.10. As a result, I've
bumped the minimum required versions of AT-SPI2 and ATK from 2.10 to
2.12. I've also started using the proper math role from 2.12 which
should be more performant than the object-attribute check which was in
place.

--joanie