Adjust margin for notification_top_line in groups

With the recent changes to the collapsed layout, we're setting a special
margin for the large icon in Notification.java for
notification_top_line. We need to adjust that margin accordingly when
the right icon appears on the left instead.

Fix: 434272572
Test: manual, post a group of notifications with a long title and a
large icon and ensure the title takes up the whole space available
Flag: android.app.notifications_redesign_templates

Change-Id: I9c9fed5d3ce9052c34ed124fba4a755f9d0b6bd9