Capture screenshot for activity when canceling rotation

So shell side's ScreenRotationAnimation can animate the screenshot
based on previous rotation. Otherwise the rotation animation will
show half black because there is no content for the exit animation.

Bug: 303418928
Bug: 304151825
Test: Enable auto rotation. Launch an app without fixed
      orientation from portrait launcher while device is
      in landscape. Before the launch animation is done,
      rotate the device to portrait (there is no display
      orientation change). There should be a smooth rotation
      animation for landscape to portrait on activity level.
Change-Id: I04a8f0ac451e81f0687faf95daed673debb2bc8e