feat(v2): add fonts loaders + webpack resolve.roots

[slorber]

Motivation

After upgrading css-loader here: #4081

The url(/my/font.ttf) are not resolved by Webpack, while it was not the case before.

Exemple in:

@font-face {
  font-family: "Iran Sans";
  font-style: normal;
  font-weight: 100;
  src: url("/fonts/IRANSans5.5/IRANSansWeb_UltraLight.eot"),
    /* IE9 Compat Modes */
      url("/fonts/IRANSans5.5/IRANSansWeb_UltraLight.eot?#iefix")
      format("embedded-opentype"),
    /* IE6-IE8 */ url("/fonts/IRANSans5.5/IRANSansWeb_UltraLight.woff2")
      format("woff2"),
    /* Super Modern Browsers */
      url("/fonts/IRANSans5.5/IRANSansWeb_UltraLight.woff") format("woff"),
    /* Modern Browsers */ url("/fonts/IRANSans5.5/IRANSansWeb_UltraLight.ttf")
      format("truetype");
} 

The CSS above now fails to build, because /fonts/IRANSans5.5/IRANSansWeb_UltraLight.eot can't be resolved (due to not resolving from the static folder, and also because there's no loader for .eot files.

I think it's not a bad idea to go through the Webpack assets pipeline in such case (as it hash the assets, allowing easier/better caching) so we won't disable this, but need to keep the existing userland CSS retrocompatible.

More context discussed here: webpack-contrib/css-loader#1256

Have you read the Contributing Guidelines on pull requests?

yes

Test Plan

Tested locally using a site using the CSS above:
https://github.com/massoudmaboudi/datagit_v2.docusaurus

After this change, the site can now build again after upgrading Docusaurus while it can't without this change.

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[V1] Deploy preview success

Built with commit c0e12b5

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Size Change: +13 B (0%)

Total Size: 156 kB

ℹ️ View Unchanged

Filename	Size	Change
website/build/assets/css/styles.********.css	17.6 kB	0 B
website/build/assets/js/main.********.js	109 kB	+14 B (0%)
website/build/blog/2017/12/14/introducing-docusaurus/index.html	21.7 kB	0 B
website/build/docs/introduction/index.html	180 B	0 B
website/build/index.html	6.94 kB	-1 B (0%)

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Deploy preview for docusaurus-2 ready!

Built with commit c0e12b5

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⚡️ Lighthouse report for the changes in this PR:

Category	Score
🟠 Performance	74
🟢 Accessibility	96
🟢 Best practices	100
🟢 SEO	100
🟢 PWA	95

Lighthouse ran on https://deploy-preview-4198--docusaurus-2.netlify.app/classic/