Deserialises the JSON encoding used by Fable.SimpleJson, which is what the app writes into every .dgm file. Without this, nothing running under .NET can open a sheet, because Thoth.Json.Net - what `Helpers.jsonStringToState` otherwise uses there - cannot read what the app wrote. The two encodings disagree about unions (Thoth writes an array; SimpleJson writes a bare string for a nullary case and a single-property object otherwise), about options (Thoth wraps the value; SimpleJson writes the value itself, or null) and about maps with structural keys (SimpleJson writes an array of pairs). Rather than enumerate the `SavedInfo` schema - which would mean every `ComponentType` case, and a new one every time a component is added - this walks the target type by reflection, so it covers whatever the types say. Fable never sees any of this: under Fable the app calls SimpleJson itself, and Newtonsoft is not available. Under .NET it reaches this project transitively through Thoth.Json.Net.