Docs: Show source of corresponding args in source block

[tmeasday]

Closes #20745

What I did

• Emit args with SNIPPET_RENDERED event
• Store code in source container keyed on args hash
• Read code based on args except if __forceInitialArgs is passed to Source (in which case read on initialArgs).
• Pass __forceInitialArgs through.

How to test

See stories & E2E tests. Try changing args on docs page with source open and check only the primary story changes.

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"]

[socket-security]

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Issue	Status
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Invalid package.json	✅ 0 issues
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[JReinhold]

Code looks good.

Still concerned about this though #20745 (comment)

This would require all renderers to change right, even the community ones we don't control?

[tmeasday]

@JReinhold note the fallback to "unknown args" when we don't receive args details on the channel message.

[JReinhold]

LGTM! Only a minor nit.

[tmeasday]

@shilman as discussed, the E2E test I added here which inspects the arg value in the snippet is failing in various frameworks that don't appear to be rendering the snippet (should contain something like label="Basic") correctly:

Angular:

<storybook-framework-button
  label=\"false\"
  (onClick)=\"onClick($event)\"
  ></storybook-framework-button>

Lit:

<sb-button></sb-button>

Next: - known issue: #20356

<head_manager_provider_default>
  <No Display Name />
</head_manager_provider_default>"

In Vue it renders the right thing but never updates based on args changes. It looks like the SNIPPET_RENDERED event isn't emitted on args changes.