Generate down events when transferring touch focus

When we transfer touch focus to another window we are
now sending down events for all pointers that would
be delivered tot his window to ensure it sees a consistent
event stream.

Bug:146535667

Test: atest CtsAutofillTestCases
      atest inputflinger_tests
      atest com.android.server.wm.DragDropControllerTests
      atest android.server.wm.DragDropTest
      atest android.server.wm.CrossAppDragAndDropTests

      added dedicated tests to inputflinger_tests

Change-Id: Ic745df966dbd873da94bb6d8061552ce1a5b27b0