Dart is migrating to .dart_tool/ as the location for cached artifacts
and other temporary files generated by tooling in the SDK. As part of
this, pub will be migrating from .pub to .dart_tool/pub.
In future, this path will also be used for other tooling, such as package:build.
Allows the user to specify the kind of project to create. The default is 'app'. Other choices are 'plugin' (the old '--plugin' behavior), and 'package'.
A Flutter 'package' is a Dart package that depends on Flutter, but does not contain native code.
Fixes#10377.