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Shift Recents task to top when opening Recents.
Unlike usual opening/closing app transition, the Recents task should above Home task when opening recents, otherwise the home task would above the recents task so it will seems like the home been add into recents animation. Bug: 207297486 Test: enable shell transition, setup 3rd-party launcher as default home. Entering recents at home page and verify the home task won't stay on top. Change-Id: I9bac97cb79febf112ec9ac1bdbe3de205604b01d