Developer documentation
Design doc

To take into consideration:

• 3 separate variable fonts for outlined, rounded, and sharp styles
• advantages provided by using a variable font
• possibly not using static consts

Related issues:

• automatic updating (Automatic Icons Updater for Flutter #83741)
• providing them in a package (Make Material Icons font a package  #12569)
• better integration with IDEs (Use a more resilient mechanism for showing the icons on the Icons page #11073, Support icon previews in editors via the analysis server dart-lang/sdk#47667), could store data in https://github.com/flutter/tools_metadata
• Icons to Enum #104987