Allow populating left_icon independently of right_icon.

* Mainly this fixes a "bug" with the BigPictureStyle.showBigPictureWhenCollapsed() that would cause the big picture, which is known to be important for the notification, to be hidden on the right and shown on the left.  Instead the BigPicture will now remain visible in its large form on the right, and the left icon will be populated with the large icon.
* Additionally, this fixes some quirks with other layouts, such as MediaStyle and MessagingStyle that the largeIcon would be missing (sometimes only in one expansion state) when it could be shown in the left column.
* Finally, this fixes a few bugs in the expansion animation that were caused by logic for determining the showing icon being inconsistent between Notification.java and the notification view wrappers.

Bug: 186421651
Test: post notifications of all these types in and outside of groups.
Change-Id: Ifd1d817afcb1b6fa8cfb79baee96364af8c7af3c