Show LargeIcon as wide for apps targeting S.

* This does not inhibit the grouping behavior which demotes this image and shows it in a smaller square area on the left.
* This also converts the Notification class to calculate margins and sizes in DIP instead of PX, as that is more resilient.

Fixes: 175409684
Test: atest NotificationTemplateTest
Change-Id: I35d28c8df341dbbac2774026c6ca749e296c0482