[heycam/webidl] Bad interaction between [Replaceable] and [LegacyLenientThis] causes an assertion failure when the setter is called on a primitive (#916)

The following snippet demonstrates the issue:
```webidl
[Exposed=Window]
interface Foo {
 [Replaceable, LegacyLenientThis] readonly attribute any attr;
};
```

```js
Object.getOwnPropertyDescriptor(Foo, 'attr').set.call(123);
```

## Expected behaviour:
Either throw a `TypeError` or return `undefined`.

## Actual behaviour:
Because of **Step 4.5.5.1** in [attribute setter][dfn-attribute-setter]:

> 1. Let <var>esValue</var> be the **this** value, if it is not **null** or **undefined**, or <var>realm</var>’s [global object][concept-realm-global] otherwise. (This will subsequently cause a <code>[TypeError]</code> in a few steps, if the global object does not implement target and <code>\[[LegacyLenientThis]\]</code> is not specified.)
> 2. If <var>esValue</var> [is a platform object][is-a-platform-object], then [perform a security check][dfn-perform-a-security-check], passing <var>esValue</var>, <var>id</var>, and "setter".
> 3. Let <var>validThis</var> be **true** if <var>esValue</var> [implements] <var>target</var>, or **false** otherwise.
> 4. If <var>validThis</var> is **false** and <var>attribute</var> was not specified with the <code>\[[LegacyLenientThis]\]</code> [extended attribute][dfn-extended-attribute], then [throw] a <code>[TypeError]</code>.
> 5. If <var>attribute</var> is declared with the <code>\[[Replaceable]\]</code> extended attribute, then:<ol><li>Perform [?] [CreateDataProperty]\(<var>esValue</var>, <var>id</var>, <var>V</var>\).</li><li>Return **undefined**.</li></ol>
> 6. If <var>validThis</var> is **false**, then return **undefined**.

[CreateDataProperty] gets called unconditionally on the passed <var>esValue</var>, but <var>esValue</var> may contain a primitive value if <code>\[[LegacyLenientThis]\]</code> was also specified, which causes an [Assert] failure in **Step 1** of [CreateDataProperty].

[?]: https://tc39.github.io/ecma262/#sec-returnifabrupt-shorthands

[Assert]: https://tc39.es/ecma262/#assert

[CreateDataProperty]: https://tc39.github.io/ecma262/#sec-createdataproperty

[LegacyLenientThis]: https://heycam.github.io/webidl/#LegacyLenientThis

[Replaceable]: https://heycam.github.io/webidl/#Replaceable

[TypeError]: https://tc39.es/ecma262/#sec-native-error-types-used-in-this-standard-typeerror

[concept-realm-global]: https://html.spec.whatwg.org/multipage/webappapis.html#concept-realm-global

[dfn-attribute-setter]: https://heycam.github.io/webidl/#dfn-attribute-setter

[dfn-extended-attribute]: https://heycam.github.io/webidl/#dfn-extended-attribute

[dfn-perform-a-security-check]: https://heycam.github.io/webidl/#dfn-perform-a-security-check

[implements]: https://heycam.github.io/webidl/#implements

[is-a-platform-object]: https://heycam.github.io/webidl/#is-a-platform-object

[throw]: https://heycam.github.io/webidl/#ecmascript-throw


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