- It is entirely derived from `SkinLayoutInfo.DrawableInfo`, which is
the actual primary thing we want to serialise.
- It will never get read out from any serialised files anyway (corollary
of the previous point - it is a get-only property derived from another).
- It is only used in tests.
All of the three reasons above make serialising the property out to skin
files nothing more than a waste of space.
Functionally equivalent right now, but the combined variant is more
localised to what it actually needs to do, and less error-prone if
any new code gets appended to the method.