Let a value be a bundle of named fields

PropertyValue was number | string | boolean | list. A struct joins it, which
costs two things the typechecker found rather than I did.

An object on a data edge used to mean a live entity, so asEntity would have
taken a struct for one and asString would have read .name off it. EntityHandle
now carries a symbol brand – a symbol so no field name can impersonate it, and
it never serializes, which suits a thing that exists only while the game runs.
It is built in exactly one place.

String(value) would have written a struct as [object Object] at 39 call sites.
They go through textOf(), which is identical for primitives.

normalizeGraph dropped everything but primitives from node params, so the List
node lost its value on every save ([3,1,4] round-tripped to undefined).
Variables were spared: they have a schema, params have none.

src/editor/texture/TextureCanvas.ts

@@ -8,7 +8,7 @@ import {
 } from 'pixi.js';
 import { AddFrameCommand, SetFrameRectCommand } from '../../core/commands/frameCommands';
 import type { TextureAsset, TextureFrame } from '../../core/model/Asset';
-import type { Vec2 } from '../../core/model/Properties';
+import { textOf, type Vec2 } from '../../core/model/Properties';
 import { findAsset } from '../../core/model/Project';
 import { type FrameRect, MIN_FRAME_SIZE, normalizeFrameRect } from '../../core/model/texture';
 import { type Size, Theme, textStyle, ui, Widget, zoomFactor } from '../../ui';
@@ -335,7 +335,7 @@ export class TextureCanvas extends Widget {
   private pictureOf(asset: TextureAsset) {
     return textureLibrary.get({
       file: asset.file,
-      smooth: String(asset.props.filter ?? 'linear') !== 'nearest',
+      smooth: textOf(asset.props.filter ?? 'linear') !== 'nearest',
       rect: null,
       sourceWidth: asset.width,
       sourceHeight: asset.height,