Execute transition by starting window only if it is forward type

Otherwise if the onStartingWindowDrawn is called for a transferred
starting window, it may be too early to execute the close transition
which is triggered by previous finishing trampoline activity.

Bug: 206513982
Test: setprop persist.debug.shell_transit 1; reboot
      atest StartActivityTests#testStartActivityFromFinishingActivity
Change-Id: I4ff020384092b2c95ca9038a9a3fcb7515f398d5