* Add TaggedValue::TypeDefault to avoid baking placeholder Tables into saved documents
* Add TaggedValue::TypeDefault to avoid baking placeholder Tables into saved documents
* Migrate empty Vector/Raster/Graphic/Artboard placeholder values to TypeDefault on load
Documents written before the TypeDefault mechanism existed have empty Table<Vector>/<Raster>/<Graphic>/<Artboard> values baked into every unwired exposed input. Walk each migrated node's inputs and rewrite any such placeholder NodeInput::Value into the equivalent NodeInput::type_default, so re-saved documents shed the placeholder payloads. Marked with a TODO for eventual removal once enough documents have been re-saved.
* Re-save demo artwork
* Remove Graphic and Artboard placeholder containers from TaggedValue
* Remove Raster placeholder TaggedValue variant
* Simplify document migration
* Remove Vector placeholder TaggedValue variant
* Remove NodeIdTable from the TaggedValue
* Remove StringTable from the TaggedValue
* Remove F64Table in place of F64Array in TaggedValue
* Replace TaggedValue::Color(Table<Color>) with ::Color(Option<Color>)
* Replace TaggedValue::GradientTable(Table<GradientStops>) with ::Gradient(GradientStops)
* Replace TaggedValue::BrushStrokeTable(Table<BrushStroke>) with ::BrushStrokes(Vec<BrushStroke>)
* Make TaggedValue::DocumentNode runtime-only with TypeDefault placeholder
* Make TaggedValue::ContextFeatures runtime-only
* Remove Serialize/Deserialize from Table<T>
* Add a widget for TaggedValue::BrushStrokes to visualize strokes and samples
* Define a reusable list of TaggedValue::TypeDefault types for its generated methods
* Re-save demo artwork
* Move Vec<String> to Table<String>
* Remove old VecDVec2
* Move Vec<u8> to Table<u8>
* Move Vec<f64> to Table<f64>
* Move [f64; 4] to Table<f64>
* Move Vec<NodeId> to Table<NodeId>
* Tidy up the TaggedValue variants
* Move Vec<BrushStroke> to Table<BrushStroke>
* Add missing type implementations
* Fix tests
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