[Notif] Update guts/blocking helper UI

Polishing UI based on UX phase 3.

Updated font style, spacing, header alignment, button tap target (8dp
onsides, 14dp on top/bottom for 48dp touch target).

Double checked that other views that share in the button tap
targets/styles weren't affected negatively.

Test: visually
Bug: 77318740
Change-Id: I71cd0187b6d9d6cce62e0051af84922594bc5a9a