Mobs do not support hat layer armours

Partner Rank:
2

Verification builds:
1.11.402.0 2242720

Summary:
Armour on entities does not render the hat layer

Impact:
This affects Tiny footprints as it incorrectly renders the helmets. In the case of Iron and Diamond they appear invisible which can cause confusion.

Repro Steps:

1. Download TinyFootprints from the store
2. Download custom Behaviour pack attached below
3. Create a creative world with Tinyfootprints + behaviour pack equipped
4. Equip a gold helmet
5. Spawn Skeletons  
6. Observe they are rendered differently
7. Open up loot_table json and change all golden values to diamond
8. Reopen world and spawn skeleton
9. Observe no diamond helmet visible 

Observed Results:
The hat layer is not rendered on mobs.

Expected Results:
The hat layer is rendered much like on armour and armour stands

Screenshots/Videos attached:
Yes

Regression Builds:
Since inception

Notes:
Within TinyFootprints texture pack the diamond and iron helmets are on the hat layer for better visuals. As hat layers are not rendered it appears invisible which confuses players why a skeleton which should appear to burn does not. 
Within the screenshot my skin is a zombie in the Tinyfootprints style, noted to prevent confusion. The golden armour renders correctly on my player.