New hot API

[theKashey]

This PR is aimed to solve 2 issues:

• there no way to configure errorReporter using hot - there were several issues about it, like Example Error Boundary #1111
• in case of JS error out of RHL scope we are not charging a new module.hot.accept and that's lead to full page reload next time - Hot reloading shouldn't stop after an error #1078

The change

• split hot into two pieces

import {hot} from 'react-hot-loader/root';
//^^ this will setup HMR for the "parent"(current) module, and then wipe itself from a cache, to execute the same action for the next call

export hot(Component);
// ^ this call is a bit shorter, and does not use magic `module` variable.

If "first" part is called, but second is not - then some JS error took a place, and we should display an Error overlay.

[codecov-io]

Codecov Report

Merging #1122 into master will decrease coverage by 0.83%.
The diff coverage is 64.03%.

@@            Coverage Diff             @@
##           master    #1122      +/-   ##
==========================================
- Coverage   84.89%   84.05%   -0.84%     
==========================================
  Files          33       37       +4     
  Lines        1026     1154     +128     
  Branches      258      281      +23     
==========================================
+ Hits          871      970      +99     
- Misses        121      143      +22     
- Partials       34       41       +7

Impacted Files	Coverage Δ
src/utils.dev.js	92.3% <ø> (ø)	⬆️
src/configuration.js	100% <100%> (ø)	⬆️
src/proxy/createClassProxy.js	97.48% <100%> (+0.06%)	⬆️
src/global/modules.js	100% <100%> (ø)	⬆️
src/index.dev.js	100% <100%> (ø)	⬆️
src/global/generation.js	100% <100%> (ø)	⬆️
src/reconciler/hotReplacementRender.js	86.95% <100%> (ø)	⬆️
src/AppContainer.dev.js	88.46% <100%> (+7.5%)	⬆️
src/reactHotLoader.js	81.66% <33.33%> (+24.88%)	⬆️
src/reconciler/fiberUpdater.js	35.29% <35.29%> (ø)
... and 11 more

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[theKashey]

Next step - on hotUpdateEnter amend every mounted (tracked in createProxy) component with componentDidCatch, and remove all clean components on hotUpdateLeave, keeping only dirty ones with ErrorOverlay displayed in place.
That would match principles

[gregberge]

I think it is very nice to simplify API and to remove the magic "module" part! Good job!
I can't review it in detail because I no longer understand the whole code.

[theKashey]

@neoziro - you know - I do have the same problem. Sometimes I am thinking to start everything, especially tests, from scratch.