Add UIManager:discardEvents(), to allow dropping events
for a period of time.
Default duration of 600ms on eInk, 300ms otherwise.
Used when showing the dict result window, so that a tap
happening just when it's being shown won't discard it.
Used with Trapper:confirm()/:info(), to avoid taps made
in a previous processing to dismiss (and so, select the
cancel action) a ConfirmBox not yet painted/visible.
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