AccessibilityInfo::announceForAccessibility fails to announce

[acoates-ms]

The code to attempt to get an automation peer for the current window calls FrameworkElementAutomationPeer::FromElement on an element, but it always returns null.

We should work out how to successfully get a peer from XAML.

(This code will be checked in with #5849)

[chiaramooney]

Would advocate to move this issue to 0.65 target. With creating a comprehensive preview of RN Gallery and effectively auditing all community modules (#6444 ) as key priorities, lack bandwidth to complete this issue in time for 0.64 release.