Implement scaling for display entities

[DrZoddiak]

Implements #setScale for Display Entities since they allow for scaling in 3 directions.

[boxbeam]

yes good

[avaruus1]

How does this differ from setting the scale through the Transform or is it just a different way of doing the same thing?

[DrZoddiak]

How does this differ from setting the scale through the Transform or is it just a different way of doing the same thing?

Effectively it's the same thing. Interpolation keys still effect the entity. This PR simply implements a method that already exists but has no implementation.

Sponge/src/mixins/java/org/spongepowered/common/mixin/api/minecraft/world/entity/EntityMixin_API.java

Lines 147 to 155 in 994fb27

	@Override
	public Vector3d scale() {
	return Vector3d.ONE;
	}
	@Override
	public void setScale(final Vector3d scale) {
	// do nothing, Minecraft doesn't properly support this yet
	}

[gabizou]

One small nit, and I'm good with merging.