Storybook: Update to latest 5.3

[ItsJonQ]

This update bumps Storybook to the latest 5.3.2 release. Some of the core .js
files have been renamed and refactored according to their 5.2.x -> 5.3
migration guides.

This update also start some Storybook theming, adding the WordPress branding
logo on the top left.

#branding

The WP logo is being served from a URL. Originally, I tried to serve the image locally. However, I don't think it's working correctly with Storybook.

storybookjs/storybook#5878
storybookjs/storybook#6521

Maybe able to resolve this with Webpack work-arounds?

How has this been tested?

Run storybook locally via npm run storybook:dev. Also did a local build via npm run storybook:build. I tested the local dist build of storybook separately to ensure that it will work when built/deployed.

Types of changes

• Bump Storybook dependencies from 5.2.4 -> 5.3.2
• Adjusted main Storybook files according to their migration guides
• Added WP logo 🙌

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.
• I've updated all React Native files affected by any refactorings/renamings in this PR. .

[epiqueras]

We still need to deal with:

• We've deprecated the ability to specify the hierarchy separators (how you control the grouping of story kinds in the sidebar). From Storybook 6.0 we will have a single separator /, which cannot be configured.
• In 5.3, the CSF loader decouples the story's name/id, which means that displayName is no longer necessary. Unfortunately, this is a breaking change for any code that uses the story name field. Storyshots relies on story name, and the appropriate migration is to simply update your snapshots. Apologies for the inconvenience!

[ItsJonQ]

@epiqueras I just pushed the updates to the main.js config. I've also updated the separators (previously |) to the new Storybook standardized /.

[epiqueras]

Thanks, we still need to update the snapshots.

[ItsJonQ]

@epiqueras Oh! Thanks for the reminder <3
I'm working on that now. Jest is throwing some DOM related errors. Not sure what's causing that.

Will keep investigating

Update: Fixed. I think it's the | -> /

[epiqueras]

You need to mock the refs.

[ItsJonQ]

Rebasing with latest master

[gziolo]

https://travis-ci.com/WordPress/gutenberg/jobs/275074009#L398

It looks like types checking errors for some unknown reasons.

[ItsJonQ]

@gziolo Interesting 🤔. I'm not sure what's up with that. I'll poke at it to see if I can debug.

Thank you!!

[ItsJonQ]

@gziolo Halloo!! I think I fixed it 🙏 . I installed the latest @types/jest as a devDependency. It looks like the project didn't have it. I think the type definitions were failing because an older version of @types/jest may have been a dependency of another dependency.

I based this fix off of this GH issue:
testing-library/jest-dom#152

[ItsJonQ]

Thanks for the review @epiqueras !! Will merge 💪