Use offset relative to window instead of coords in DrawInContainer

This CL moves the computation of the position of the container and
elements to be drawn in the container during placement, using the
position relative to the window. See b/389037232#comment9 for details
on why this is necessary.

Bug: 389037232
Test: Manual, the LS => Notif shade in STL demo overscrolls as expected
Flag: com.android.systemui.scene_container
Change-Id: I8f8060838521bfb5518c2f81b0cc2c878335fca9