Upgrade to CFPB Design System 3.0

[chosak]

This PR upgrades the CFPB Design System to version 3.0.x. It drops use of Avenir Next in favor of Arial.

To test, try yarn watch and visit http://localhost:8080.

See #46 and https://github.local/Design-Development/Design-and-Content-Team/issues/502 for context.

Notes

Compilation produces the following warning:

(node:41667) [DEP_WEBPACK_COMPILATION_ASSETS] DeprecationWarning: Compilation.assets will be frozen in future, all modifications are deprecated.
BREAKING CHANGE: No more changes should happen to Compilation.assets after sealing the Compilation.
Do changes to assets earlier, e. g. in Compilation.hooks.processAssets.
Make sure to select an appropriate stage from Compilation.PROCESS_ASSETS_STAGE_*.
(Use node --trace-deprecation ... to show where the warning was created)

This is due to this line in the nunjucks-webpack-plugin plugin used by this repository. Unfortunately that package seems abandoned; it would be better long-term to migrate this website to esbuild and some other templating strategy. For now this is the minimal change needed to migrate to DS v3.

Checklist

• PR has an informative and human-readable title
• Changes are limited to a single goal (no scope creep)
• Code can be automatically merged (no conflicts)
• Passes all existing automated tests

[anselmbradford]

This LGTM! 👍 THANKS!!