Add support for Brotli compression

[clupprich]

Adds support for Brotli compression via the compression-webpack-plugin package/plugin when running Node versions >=11.7.0, as described in #2089.

I could use some help in writing tests for this - any good starting points?
I'm also not really happy about the added dependency on the semver package - maybe some small utility function would do the trick here? Fixed that in 716ac1d by checking the presence of process.versions.brotli.

[clupprich]

Ah, Brotli has its own entry in process.versions, I can probably use that. Thanks to @julianrubisch for that hint!

[guillaumebriday]

Hey!

That is so cool, thank you @clupprich 👍

I think we should add configuration example and installation details in the https://github.com/rails/webpacker/blob/master/docs/deployment.md?

What do you think?

Thanks

[clupprich]

@guillaumebriday Definitely! Do you think we should also add a config flag to enable/disable this? Because Brotli isn't widely supported yet by e.g. hosted solutions (Heroku, afaik), this can be overhead that people don't need.

[guillaumebriday]

I think we should not add a specific config option only for Brotli even if it's not supported by some hosted solutions. These solutions will simply ignore the Brotli files.

I think, we can add sentence like that but for Brotli:

Some servers support sending precompressed versions of files with the .gz extension when they're available. For example, nginx offers a gzip_static directive.

And add a link (or steps) to install it with a warning on the minimal node version required.

What do you think?

[clupprich]

Added the instructions in f70f7ef. Turns out the hard part is not the code, but the documentation ;). Let me know if that section makes sense.

[guillaumebriday]

It makes sens ! The google's instructions are not very clear imo.

I think this line should be removed.

[clupprich]

🤦‍♂

[gauravtiwari]

Thanks @clupprich

[clupprich]

🎉 Thanks @guillaumebriday and @gauravtiwari

[guillaumebriday]

🎉