New lint: potential bug with assigning a value to a tracked property

Example:
```js
class Demo extends Component {
@tracked foo = this.someProperty

@cached
get someProperty() {
return this.args.someData ?? [];
}
}
```

The bug is that we expect `foo` to initially be `someProperty`, but `someData` may not yet be available and we end up setting `[]` as the value of `foo` on first render.

Since property assignment is _non-reactive_, we should warn of this bug, and suggest using `@localCopy` from https://github.com/tracked-tools/tracked-toolbox
so that changes to `someProperty` used in `foo`