This commit makes the label accessible implement AtkHypertext,
which returns a AtkHyperlink object for each link in the text.
At the same time, add AtkHyperlinkImpl objects as children
to the label accessible.
Also some private API to indicate that links have changed, and
call that from GtkLabel when needed.
Adjust expected output of the affected a11y tests.
https://bugzilla.gnome.org/show_bug.cgi?id=721410https://bugzilla.gnome.org/show_bug.cgi?id=721421
This reverts commit 7cecc8e524.
It is impossible to use the selection object of the menu while it is
collapsed (collapsed menus deselect everything for a start), so even
though the original patch was correct, the followup issues are too big
to solve this quickly to a release.
https://bugzilla.gnome.org/show_bug.cgi?id=707786
