Default mob armor

Status
Fixed
Issue description

Some vanilla mobs (zombies, magma cubes, the wither, the Shulker when closed and the killer rabbit) have a default amount of armor points.

It would be cool to give custom mobs some armor points without actually giving them armor pieces.

Issue comments

Right now you can do this in the code by adding this in the mob entity constructor:

this.getEntityAttribute(SharedMonsterAttributes.ARMOR).setBaseValue(2.0D);