Updating Material Design Fonts & Icons

The process to update the framework's Material fonts (currently, Roboto) and icons has been largely simplified and automated. See go/effortless-flutter-font-updates (Google-only, sorry). The steps used prior to automation are available in this page's history.

If you notice an issue with fonts or icons (e.g. a missing icon), please file an issue. Consider starting the issue title with [Fonts] or [Icons] to make it stand out.

(This page is referenced by comments in the Flutter codebase.)