[@sheet] Do we want to be able to access sheets declared in shadow DOM from light DOM?

Do we want to be able to access sheets declared in shadow DOM from light DOM? For example:

```html
<template shadowrootmode="open">
  <style>
    @sheet foo {
      div {
        color: red;
      }
    }
  </style>
  <link rel="stylesheet" href="#foo" />
  <span>I'm in the shadow DOM</span>
</template>

<link rel="stylesheet" href="#foo" />
<span>I'm in the light DOM</span>
```