Docs: Allow ArgTable usage unattached

[tmeasday]

Closes #21366

What I did

Rework legacy ArgsTable to work even if storyById() throws (unattached).

How to test

1. yarn task --task dev --template lit-vite/default-ts
2. Add <ArgsTable of="button" /> to Introduction.mdx
3. Visit http://localhost:6006/?path=/docs/example-introduction--docs

Checklist

• Make sure your changes are tested (stories and/or unit, integration, or end-to-end tests)
• Make sure to add/update documentation regarding your changes
• If you are deprecating/removing a feature, make sure to update
  MIGRATION.MD

Maintainers

• If this PR should be tested against many or all sandboxes,
  make sure to add the ci:merged or ci:daily GH label to it.
• Make sure this PR contains one of the labels below.

["cleanup", "BREAKING CHANGE", "feature request", "bug", "documentation", "maintenance", "dependencies", "other"]

[tmeasday]

@shilman I think this code is theoretically right, but I am getting (with the instructions above):

I'm pretty sure that makes sense because "button" is not a reference to a component 🤷

[shilman]

@tmeasday You can use the component demo-wc-card and it's working

[JReinhold]

LGTM!