Dart-only platform implementations

In some cases, some platforms can be
implemented entirely in Dart (for example, using FFI).
For a Dart-only platform implementation on a platform other than web,
replace the pluginClass in pubspec.yaml with a dartPluginClass.
Here is the hello_windows example above modified for a
Dart-only implementation:

flutter

plugin

implements

hello

platforms

windows

dartPluginClass

HelloPluginWindows

In this version you would have no C++ Windows code, and would instead
subclass the hello plugin’s Dart platform interface class with a
HelloPluginWindows class that includes a static
registerWith() method.  This method is called during startup,
and can be used to register the Dart implementation:

class

HelloPluginWindows

extends

HelloPluginPlatform