feat(plugin-webpack): add an option to export webpack compilation stats

[sirgallifrey]

BREAKING CHANGE:
This Feat is opt-in, so probably there is no breaking changes.

ISSUES CLOSED: #591

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• The changes are appropriately documented (if applicable).
• The changes have sufficient test coverage (if applicable).
• The testsuite passes successfully on my local machine (if applicable).

Summarize your changes:

Added two new options for webpack plugin, one for the main process and one for the renderer process.
If they are set to true, a stats.json file will be created respecting the webpack.stats config.

[sirgallifrey]

I tried to rebase my mistakes away and ended up with two commits anyway... :(
Do I rebase again and force push them?

[malept]

Don't worry about it. On merge it will likely be squashed.

[malept]

We probably want a test for this but I don't know exactly what it looks like.

[sirgallifrey]

I'll give a shot on some tests, but they will probably be integration or functional tests since the code looks tightly coupled.

[malept]

I'd prefer a functional test over an integration test. The tests take a while to run as it is.

[sirgallifrey]

Testing on this plugin is hard to reason about and will likely to get convoluted :(
Would you be open for some refactoring on this plugin to break its functionalities in smaller classes so we can make cleaner tests?

[malept]

cc @MarshallOfSound as he wrote the webpack plugin

[malept]

This is good enough for now.

We do need to figure out a good way to test the compile steps in general, at least.

Thanks for your patience!