Add horizontal dividers to UI per mocks

Above and below the actions row.

Extracted the actions row layout to be an include to reduce duplication
a bit without restructuring.

Colors and padding will likely change later.

Bug: 277745495
Test: Trigger different preivew UIs via ShareTest, validate that
      dividers show up.
Change-Id: I16d60554d0c060f6472907f8557366344f22ddc3
4 files changed