Selectively autoexpand bundles

Autoexpand a bundle if it's the only bundle and it only has
one child (notif or group). The child in the bundle should not
be autoexpanded in this case

Also - spec change - omit the number from the bundle expander when it's
expanded

Test: RowAppearanceCoordinatorTest
Fixes: 435698976
Flag: com.android.systemui.notification_bundle_ui
Change-Id: I52f17ad74d4d6b3e2fb4fc5e7cdc09da558dca94