Feature: Extend setAddon API

[usulpro]

The current API:

setAddon({ addonA(), addonB() }) 

It adds addons to storiesOf() object and they accessible as methods:

storiesOf(...)
  .addonA()
  .addonB()

Why we need new API

Sometimes we want to implement some features or some behavior to storiesOf() to have it by default. This would open up a plenty new directions in the addons creation!

What I did

Just allow passing into setAddon functions matching /^_init/ and make them executed right after storiesOf() is created.
This is a backward compatible change, addons with normal names still work the same.

New API

setAddon({ addonA(), addonB(), _initSmth() }) 

when you create:

storiesOf(...)
  .addonA()
  .addonB()

_initSmth() will not be accessible as a method of storiesOf() but it will be already executed

How to test

run cra-kitchen-sink
check out the Toc first story of each storyKind (it just an example of how it works)
check that other addons work as usual

[codecov]

Codecov Report

Merging #1463 into release/3.3 will decrease coverage by 6.39%.
The diff coverage is 77.77%.

@@              Coverage Diff               @@
##           release/3.3    #1463     +/-   ##
==============================================
- Coverage        22.32%   15.93%   -6.4%     
==============================================
  Files              324      237     -87     
  Lines             6319     5051   -1268     
  Branches           803      629    -174     
==============================================
- Hits              1411      805    -606     
+ Misses            4297     3715    -582     
+ Partials           611      531     -80

Impacted Files	Coverage Δ
app/react/src/client/preview/client_api.js	83.33% <77.77%> (-2.39%)	⬇️
...s/stories/required_with_context/Welcome.stories.js	0% <0%> (-100%)	⬇️
...dons/storyshots/stories/directly_required/index.js	0% <0%> (-100%)	⬇️
...ts/stories/required_with_context/Button.stories.js	0% <0%> (-100%)	⬇️
addons/info/src/index.js	0% <0%> (-90.91%)	⬇️
addons/storyshots/src/index.js	0% <0%> (-80.86%)	⬇️
lib/ui/src/modules/ui/components/search_box.js	16.66% <0%> (-77.28%)	⬇️
addons/info/src/components/Story.js	0% <0%> (-76.2%)	⬇️
lib/ui/src/modules/ui/containers/search_box.js	33.33% <0%> (-66.67%)	⬇️
addons/info/src/components/markdown/text.js	0% <0%> (-66.67%)	⬇️
... and 226 more

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[shilman]

Super interesting idea. However, personally I'd vote against expanding the API at all until we get the existing API working better.

[usulpro]

This approach can help us to get rid of global decorators:

Instead of adding them globally addDecorator can add them after storyKind is created

[danielduan]

Closing this because there hasn't been any activity here for a while. Feel free to reopen when this is ready for discussion again.