Migrate addon backgrounds to TS

[gaetanmaisse]

Issue:

#5030

What I did

• Migrate @storybook/addon-backgrounds to TypeScript
• Refactor some imports/exports
• Add some types and interfaces and use them to type codebase
• Rename src/Tool.js to containers/BackgroundSelector.ts
• Export ColorIcon in its own file components/ColorIcon.ts

[gaetanmaisse]

⚠️ Build will fail, due to TS compilation errors, until #5534 will be merged

[Keraito]

Looks good!

[Keraito]

Your changes at https://github.com/storybooks/storybook/pull/5535/files#diff-f01e7bd996316ee937af51de4ab40f37R30 are not quite the same as the original. The original would be right? any, while yours is actually right: any since you're always setting the right property.

Also: Do we not have config in place to type this as a React/JSX element?

[codecov]

Codecov Report

Merging #5535 into next will decrease coverage by 0.05%.
The diff coverage is 0%.

@@            Coverage Diff            @@
##            next    #5535      +/-   ##
=========================================
- Coverage   33.1%   33.05%   -0.06%     
=========================================
  Files        638      640       +2     
  Lines       9264     9279      +15     
  Branches    1318     1346      +28     
=========================================
  Hits        3067     3067              
- Misses      5571     5597      +26     
+ Partials     626      615      -11

Impacted Files	Coverage Δ
addons/backgrounds/src/deprecated.ts	0% <ø> (ø)
addons/backgrounds/src/containers/index.ts	0% <0%> (ø)
addons/backgrounds/src/index.ts	0% <0%> (ø)
addons/backgrounds/src/register.tsx	0% <0%> (ø)
addons/backgrounds/src/constants.ts	0% <0%> (ø)
.../backgrounds/src/containers/BackgroundSelector.tsx	0% <0%> (ø)
addons/backgrounds/src/components/ColorIcon.tsx	0% <0%> (ø)
addons/backgrounds/src/components/index.ts	0% <0%> (ø)
... and 4 more

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[ndelangen]

@gaetanmaisse I invited you to the Storybook organisation on GitHub, Would you be able to join our discord to chat?

[shilman]

@ndelangen @gaetanmaisse @tmeasday FYI I'm going to release this in 5.0 since it's blocking a couple PRs. I'd rather not release it because it was merged after "feature freeze" but i think it's faster to merge than to stick to principle on this one.