Fix NSSL bottom margin with 3-button nav and no split shade

It looks like some of the margin calculation logic in
NotificationsQSContainerController.calculateBottomSpacing got mangled
when we added split shade, so make sure there's enough space to swipe
the whole shade up even with 3-button nav and no split shade.

Bug: 222594381
Test: manual, on Pixel 5a
Change-Id: Id83298f7412d087b4b8a6211587b4ec32710315b

packages/SystemUI/src/com/android/systemui/statusbar/phone/NotificationsQSContainerController.kt

@@ -200,6 +200,7 @@ class NotificationsQSContainerController @Inject constructor(
                 containerPadding = bottomStableInsets
             } else {
                 containerPadding = 0
+                stackScrollMargin = bottomStableInsets + notificationsBottomMargin
             }
         }
         val qsContainerPadding = if (!(isQSCustomizing || isQSDetailShowing)) {

packages/SystemUI/tests/src/com/android/systemui/statusbar/phone/NotificationQSContainerControllerTest.kt

@@ -206,7 +206,9 @@ class NotificationQSContainerControllerTest : SysuiTestCase() {
         given(taskbarVisible = false,
                 navigationMode = BUTTONS_NAVIGATION,
                 insets = windowInsets().withStableBottom())
-        then(expectedContainerPadding = 0, expectedQsPadding = STABLE_INSET_BOTTOM)
+        then(expectedContainerPadding = 0,
+                expectedNotificationsMargin = STABLE_INSET_BOTTOM + NOTIFICATIONS_MARGIN,
+                expectedQsPadding = STABLE_INSET_BOTTOM)
     }
 
     @Test