Fenced code blocks inside of a block component lose their top-level indentation

[adamdehaven]

I believe I have a valid fix for this over at nuxt-content/remark-mdc#143

---

Reproduction

Paste this MDC into the sandbox

::container

  ::container
  ---
  foo: "bar"
  ---
  ::

```json
{
  "labore": "set dolore",
  "magna": "aliqua",
  "veniam": true
}
```

::

Notice the missing indentation on the json fenced code block: