Log Message:
Update at-spi2-atk to 2.16.0

* Add roles for fractions, roots, subscripts, and superscripts.
* Add action tests (bgo#743418).
* Don't parse non-existent signal arguments from atk.
* Support ATK_STATE_HAS_TOOLTIP (bgo#738953).
* Support ATK_STATE_READ_ONLY (bgo#690008).
* Add mapping between ATK_ROLE_STATIC and ATSPI_ROLE_STATIC