[1.9] Armour stands do not display hat layers on armour

Partner Rank: 2

Summary:
The armour stand no longer supports the hat layer. This leads to the helments in Tiny Footprints appearing invisible 

Impact:

The texture is not displayed leading to confusion and appearing broken which may lead to wanting a refund or bad reviews. Players may believe they lost their helmet and be disgruntled 

Repro Steps:

1. Download Tiny Footprints from Store
2. Create a world in creative
3. Place an armour stand and equip diamond armour on it  
4. Observe the helmet is invisible, right clicking to remove the armour will take the helmet off 

1. Rerun the same test in 1.8.0 Client 
2. Observe a helmet is visible 

Observed Results: 

The armour stand no longer supports the hat layer on armours 

Expected Results: 
The armourstand supports the hat layer on armour like previously

Screenshots/Videos attached: 
Yes

Regression Builds:

1346382 1.8.0.21 

Notes

This issue also affects other mobs with armour on I believe. For a while the second layer of gold armour helmet had not rendered on mobs like skeletons. Therefore, it may be the case that the diamond (and other) helmets do not render on other mobs too but have not been noticed until now. They would therefore appear to be able to walk in sunlight without burning

See MCM-159 for previous related bug