Add VoiceOver announcements for child-frame completion popups and
echo-area messages.
* doc/emacs/macos.texi: Rewrite Accessibility section; add echo area
and completion suppression documentation.
* src/nsterm.h: Add child-frame and echo-area tracking ivars;
declare postEchoAreaAnnouncementIfNeeded and
announceChildFrameCompletion methods.
* src/nsterm.m (NS_AX_ECHO_SUPPRESS_SECONDS): New macro.
(ns_ax_selected_child_frame_text): New static function.
(ns_ax_maybe_refocus_after_child_frame_close): New static
function; restores VoiceOver focus to the parent buffer element
when a child frame completion popup is hidden or destroyed.
(ns_make_frame_invisible): Call refocus helper for child frames.
(ns_destroy_window): Call refocus helper for child frames.
(postEchoAreaAnnouncementIfNeeded): New EmacsView method.
(announceChildFrameCompletion): New EmacsView method.
(postAccessibilityUpdates): Major expansion; dispatch echo
area and child-frame announcements, track cursor-movement
timestamps.
(postAccessibilityNotificationsForFrame:): Clear
cachedCompletionAnnouncement when overlay candidate is nil.
(EmacsAccessibilityBuffer): Add accessibilityChildren method.
Various code quality improvements: eassert guards, specbind
inhibit-quit, memory attribute fixes.
Martin Sukany
3bce527500