@expo/webpack-config should be looking in argv for mode, not env

[dancrumb]

Summary

Per the Webpack 5 documentation, https://webpack.js.org/configuration/configuration-types/#exporting-a-function the mode property belongs on the argv object, not the env object.

While Expo itself may incorporate the non-standard approach of putting mode into env other tooling that interprets Webpack configuration files follow the API documentation, resulting in env validation failing.

Environment

N/A

Please specify your device/emulator/simulator platform, model and version

N/A

Error output

Error: @expo/webpack-config requires a valid mode string which should be one of: development, production, none

Reproducible demo or steps to reproduce from a blank project

Just run webpack without the env mode=development