Do not capture letterbox for activity snapshot.

Similar to activity window, there should draw splash screen/snapshot
starting window based on activity's bounds, so when capture activity
snapshot, the bounds should limit to activity's bounds instead of
task bounds.
While creating the windowless starting window, offset the surface
position based on activity's configuration. Also request to draw
letterbox when using windowless snapshot.

Bug: 317736686
Test: enable activity snapshot & predictive back, verify when playing
cross activity animation, the windowless surface should be place at the
same position of activity.

Change-Id: Ic3d717ef9901c30b3af7258f352d1ed21ca5bb3e