QS - Fix race condition in accessibility

When users try to open panel, initialization of accessibility is called
in Main Thread by this callstack.

at android.view.ViewGroup.buildOrderedChildList
at android.view.View.populateAccessibilityNodeInfoDrawingOrderInParent
at android.view.View.onInitializeAccessibilityNodeInfoInternal
at android.view.View.onInitializeAccessibilityNodeInfo
at android.view.View.createAccessibilityNodeInfoInternal
at android.view.View.createAccessibilityNodeInfo
at android.view.accessibility.AccessibilityRecord.setSource
...
at android.view.View.setFlags
at android.view.View.setVisibility
at com.android.systemui.qs.QSContainer.updateQsState
at com.android.systemui.qs.QSContainer.setExpanded
at com.android.systemui.statusbar.phone.NotificationPanelView.updateQsState

And another initialization is tried in QSTileHost Thread by this callstack.

at android.view.ViewGroup.buildOrderedChildList
at android.view.View.populateAccessibilityNodeInfoDrawingOrderInParent
at android.view.View.onInitializeAccessibilityNodeInfoInternal
at android.view.ViewGroup.onInitializeAccessibilityNodeInfoInternal
at android.view.View.onInitializeAccessibilityNodeInfo
at android.view.View.createAccessibilityNodeInfoInternal
at android.view.View.createAccessibilityNodeInfo
at android.view.accessibility.AccessibilityRecord.setSource
...
at android.view.View.announceForAccessibility
at com.android.systemui.qs.QSPanel.onAnnouncementRequested
at com.android.systemui.qs.QSTile.handleStateChanged

This race condition can cause crashes, because the same ArrayList
(mPreSortedChildren or mTempArrayList in ViewGroup) is modified by two
different thread.

Test : manual

Change-Id: I9e0ad1fef4be7dc378463c06d10854e0e4c5b3d6