- 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.
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