Fix issue #7401818: Wrong transition animation when clearing task

When we are clearing activities off the top of a task, propagate
any activity options down from the top-most one to whatever top
activity we are keeping.  This ensures that if we set the activity
options on the top activity of the task previously to give it the
correct animation, we still keep that animation for the activity
that really ends up being the top.

Change-Id: I6919b644a530ac283fe4d320496edc2bf72aa04e