Avoid cropping image previews.

In most cases, cropping image-based previews to just fit width leads to
degraded UX. Instead we try to fit them to the widget size if possible.

* Before: See attached bug for examples of cropped previews.
* After: http://screen/Bg7Eoydr4qBQdVZ

Additionally center align previews vertically for non-categorized
suggestions too.

Bug: 319152349, 317366201
Flag: N/A
Test: Includes a unit test & manual with the child cls
Change-Id: I4447f99028129d5d5379ead9ca404f7a011d1551