UIA: Fire live-region events

1. Added a new LIVE_STATUS_CHANGED generated event, to allow us to fire
the correct property-change event when a live-region is turned off.

2. UIA_LiveRegionChangedEventId fired when live regious are created or
changed.

3. Following the pattern established by Edgehtml, when the *first* AT
attaches, we find all our live-regions and fire a live-region change.
-- Note: This only works on Win8+; because the live-region change
event doesn't technically exist on Win7, we aren't advised of any
listeners.

Misc:
-- Implementing IRawElementProviderAdviseEvents caused Win7 to start
sending spurious focus events (even if the implementation did nothing);
these events are now filtered out.
-- The EventRecorder started hanging after I upgraded to Windows 19H1;
I implemented a quick workaround to prevent the hang; see comments.

Bug: 928949
Change-Id: Ibf34d8d66e7055c46c6a134745366249a2fef2b0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1566285
Commit-Queue: Ian Prest <iapres@microsoft.com>
Reviewed-by: Luke Halliwell <halliwell@chromium.org>
Reviewed-by: Kevin Babbitt <kbabbitt@microsoft.com>
Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#653750}
23 files changed