Add shell command to reset the frozen task state

- This can be used by tests to prevent leakage between test runs
  immediately after quickswitching (starting a quickswitch will
  freeze the recents task list for 5s)

Bug: 298544839
Test: QuickSwitchBetweenTwoAppsForwardTest
Change-Id: Ib4a5d64486ce699533c9f57c0c6faf30181a8bed