* Rename "editor:layer" to "editor:layer_path" and centralize it in a const
* Centralize "editor:merged_layers" in a const
* Centralize all other attributes in consts
* Rename consts with ATTR_ prefix
* Format
* 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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