Fixing header jump

Linking header position to an empty entry in the recyclerView,
instead of calculating the vertical scroll position. This
allows the header to be in sync with the recyclerView scroll and
item animations

Other simplifications:
> Moving top collapse handle out of header view (it doesn't scroll)
> Removing background clipping logic from full-sheet
> Moving tab bar inside the header view

Bug: 196464142
Test: Verified on device
Change-Id: Iae5a0ae9af7ce258e1b391b8e85c5c270fe56197