Revert moving index.[ios|android].js.

[tmeasday]

Issue: See #1200

What I did

Moved index.js -> index.[ios|android].js. (It didn't seem possible to make the files import index.js, I ran into this problem: facebook/react-native#6282, maybe you aren't allowed to register components from an imported file? IDK).

How to test

Follow the steps in #1200, but using npm link-ed CLI

[codecov]

Codecov Report

Merging #1201 into master will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1201      +/-   ##
==========================================
+ Coverage   13.71%   13.72%   +0.01%     
==========================================
  Files         207      207              
  Lines        4615     4611       -4     
  Branches      509      621     +112     
==========================================
  Hits          633      633              
+ Misses       3535     3434     -101     
- Partials      447      544      +97

Impacted Files	Coverage Δ
app/react-native/src/bin/storybook.js	0% <0%> (ø)	⬆️
app/react-native/src/preview/story_kind.js	0% <0%> (ø)	⬆️
addons/events/src/components/Event.js	0% <0%> (ø)	⬆️
addons/info/src/components/markdown/code.js	0% <0%> (ø)	⬆️
app/react/src/client/preview/error_display.js	0% <0%> (ø)	⬆️
...react-native/src/manager/components/PreviewHelp.js	0% <0%> (ø)	⬆️
lib/ui/src/modules/ui/configs/handle_routing.js	28.94% <0%> (ø)	⬆️
.../src/manager/containers/CommentsPanel/dataStore.js	34.78% <0%> (ø)	⬆️
app/react-native/src/bin/storybook-start.js	0% <0%> (ø)	⬆️
lib/ui/src/modules/ui/containers/left_panel.js	20% <0%> (ø)	⬆️
... and 23 more

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[shilman]

Proposal in the spirit of the original DRY change:

mv index.js storybook.js

Both index.android.js and index.android.js get:

import StorybookUI from './storybook';
export default StorybookUI;

Tested this for ios and it works.

[tmeasday]

Interesting, it didn't have the bug when I did it that way. I think maybe when I tried to make it index.js rather than storybook.js with the same content, the problem was there. Or maybe it was just RN being weird? Hopefully this works every time :/.