UI: Fix viewMode parameter handling

[ndelangen]

Issue: #10233

What I did

Made a change in lib/api/modules/stories so when navigating to a story, the parameter is read and preferred over the current state

WDYT @jonhuteau ?

[jonhuteau]

Looks good to me. So it will be possible to define viewMode in these cases ?

// my-component.stories.js

playground.story = {
  parameters: {
    viewMode: 'story',
  },
}

// my-component.stories.mdx

<Meta
  title='Packages/MyComponent'
  component={MyComponent}
  parameters={{ viewMode: 'docs' }}
/>

[shilman]

Looks good conceptually, but maybe buggy?

[ndelangen]

Seems to work to me:
https://deploy-preview-10292--storybookjs.netlify.app/official-storybook/?path=/docs/addons-docs-buttongroup--basic

Try navigating to a different story, click canvas, then navigate to that story again, it switching you to viewMode=docs