Moving now playing widget above lock icon in split shade

This change extracts lock icon padding to resources and simplifies it a bit. Also fixes small inaccuracy when reading screen size in pixels which didn't take into account status bar.
Moving margins from inner ambient to ambient container so they can be easily refreshed when layout changes.
Also moving some piece of code from AmbientContainer to NPVC as it feels a bit weird that ambient container knows about stack scroller.

Fixes: 204567063
Bug: 204567056
Test: manual
Change-Id: Ifab2980a8bfd5bf0e62b5deed85b9b811060f714