[Bluetooth] add aria-live/relevant attributes to toggle button

The Bluetooth toggle button disables itself after being pressed while
the hardware state is changing (to prevent click spamming) and
re-enables when the new state takes effect. The problem is that
Chromevox is reading the disabled state after a toggle and never
announces the updated enabled state after the hardware state is
applied. By making the element "aria-live" we request that Chromevox
announces the new state when the element state changes. This solution
results is some spammy Chromevox output, but that is better than never
announcing the state change at all.

Fixed: 1007378
Change-Id: I0632138bdea96c56edb0a0f1b9cca05d3ca2d9c2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1895255Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Commit-Queue: James Vecore <vecore@google.com>
Cr-Commit-Position: refs/heads/master@{#713539}

chrome/browser/resources/settings/bluetooth_page/bluetooth_subpage.html

@@ -48,7 +48,8 @@
       <cr-toggle id="enableBluetooth"
           checked="{{bluetoothToggleState}}"
           disabled$="[[!isToggleEnabled_(adapterState, stateChangeInProgress)]]"
-          aria-label="$i18n{bluetoothToggleA11yLabel}">
+          aria-label="$i18n{bluetoothToggleA11yLabel}"
+          aria-live="polite" aria-relevant="all">
       </cr-toggle>
     </div>