Svelte 4: $$props not working in customElement when setting properties with accessors

[ls-bit]

Describe the bug

Given a custom element component:

<svelte:options
    customElement={{
        tag: null,
    }}
/>

<script>
	export let name;
</script>

<p>$$props: {JSON.stringify($$props)}</p>
<p>$$restProps: {JSON.stringify($$restProps)}</p>

$$props and $$restProps do work when setting properties with attributes:

<ce-test name="name" other="other"></ce-test>

// output:
// $$props: {"name":"name","other":"other"}
// $$restProps: {"other":"other"}

$$props and $$restProps do not work when setting undeclared properties with accessors. Undeclared properties are missing:

const customElement = document.createElement('ce-test');
customElement.name = 'name';
customElement.other = 'other';

// output:
// $$props: {"name":"name"}
// $$restProps: {}

Related to #5482, #5608

Reproduction

https://github.com/ls-bit/svelte-ce-bug

Logs

No response

System Info

System:
    OS: Windows 11 10.0.22631
    CPU: (20) x64 12th Gen Intel(R) Core(TM) i7-12800H
    Memory: 4.74 GB / 31.68 GB
  Binaries:
    Node: 18.20.2 - ~\AppData\Local\Volta\tools\image\node\18.20.2\node.EXE
    Yarn: 4.0.0-rc.42 - ~\AppData\Local\Volta\tools\image\yarn\4.0.0-rc.42\bin\yarn.CMD
    npm: 10.5.0 - ~\AppData\Local\Volta\tools\image\node\18.20.2\npm.CMD
    pnpm: 8.15.6 - C:\Program Files\Volta\pnpm.EXE
  Browsers:
    Edge: Chromium (123.0.2420.97)
    Internet Explorer: 11.0.22621.1
  npmPackages:
    svelte: ^4.2.15 => 4.2.15

Severity

annoyance