Here's consolidating image widening into the applib repo: (including fairly comprehensive tests!)
https://github.com/wikimedia/applib/pull/8

Here's the iOS patch for using the consolidated image widening from the applib repo:
https://github.com/wikimedia/wikipedia-ios/pull/1313

Testing criteria:

( @ABorbaWMF - these may be good cases to add to the regression test list )

Examples of article images which SHOULD BE widened:

1. Most non-icon images in an article, for example, the first couple images on 'enwiki > Food':
   • Before widening (tap image for animation):
     
   • After widening (tap image for animation):
     

Examples of images in a article which SHOULD NOT BE widened:

1. Side-by-side images:
   • On 'enwiki > Vincent van Gogh > Letters', the pictures of Vincent and Theo should still be side-by-side, that is, NOT widened (tap image for animation):
     
2. Imagemap images:
   • On 'enwiki > Kingdom (biology)', the colorful hierarchy image in the lead section should NOT be widened, that is, it should appear as it does in the animation below, centered and taking up about one-third of the screen's width (tap image for animation):
     
3. Images in tables:
   • On 'enwiki > Counties of England' the images in the first collapsed table should NOT be widened (tap image for animation):
     

@cmadeo hey, skipping design review on this because it shouldn't change anything - we just moved where the code lives

Testing on iPhone 7 (iOS 10.2.1) and Wikipedia app 5.4.1 (1099). I looked at the photos @ABorbaWMF displayed above on my end,
Food is widened as expected

Tested on an iPhone 7+ with iOS 10.3 and an iPad Mini 2 Retina with iOS 10.2 both running App 5,4,1,1099

I saw the same results as Nicholas on the iPhone. Everything seemed to be fine.

On the iPad it did not appear to widen the images as seen in the example for 'Food' below. Also, there was some strange alignment on the table images.

Spoke with @Mhurd, behavior is as expected on iPad.

@Mhurd, can we close this?