Bug: 278157622
Test: Look at widget picker on tablet and verify that the colors match the new spec, and verify the portrait mode looks good also.
Change-Id: I634d876dfafc086806b233c500f7d8daddfe7b0b
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
