With accessibility mode on, hover events for a more keys keyboard are
handled among MoreKeysKeyboardAccessibilityDelegate and
MoreKeysKeyboardView. But the more keys keyboard is shown by
MainKeyboardAccessibilityDelegate that uses PointerTracker to handle
hover events. Thus we need to clear PointerTracker state when the more
keys keyboard is dismissed.

This is a workaround to resolve the issue. We should reconsider the
structure of those views and accessibility delegates in the future.

Bug: 15583751
Change-Id: Ida8c3e55194c59bdaa5bc4ff06068e699b888ced