Addon-docs: Add parameter to show code by default

[frassinier]

Issue: #10430

What I did

The property isExpanded was already available on <Canvas> block

Now you can set docs.source.state on your Addon Docs configuration!

export const parameters = {
  docs: {
    source: {
      state: 'open',
     },
  },
};

How to test

Visit https://5a375b97f4b14f0020b0cda3-wplcskzipa.chromatic.com/?path=/docs/addons-controls--basic
Where Code bocks are shown by default now.

• Is this testable with Jest or Chromatic screenshots? ✅
• Does this need a new example in the kitchen sink apps? ❎
• Does this need an update to the documentation? ✅

If your answer is yes to any of these, please make sure to include it in your PR.

[shilman]

This is great @frassinier, thank you! Made a couple small changes before merging 😉

[thien-do]

Hi :D I've just tested this in the new alpha release, and it seems it works when set:

• globally in preview.js
• page-level, like in an export default { parameters ... }

but it does not work when set:

• story-level, like Foo.parameters.docs.source.state = 'open'

[frassinier]

This PR was for Canvas, not the Story actually,
That's why we talk about global default behavior!

In MDX, at the story level, we still need to use isExpanded on Canvas which was already there!

The property isExpanded was already available on block

[thien-do]

@frassinier thank you! It seems I can also use "isExpanded" on a named exported Story in CSF?

[andrew09]

@frassinier do you mind updating the PR description for this to the updated code which shows that state: "open", is the correct key/value as opposed to state: true which the description suggests?

[dutscher]

why this isnt documented in here https://storybook.js.org/docs/react/writing-docs/docs-page ?
@shilman
cheers and thanks for the implementation