WindowsPlugin should not crash when ffiPlugin enabled (flutter#184695)

This change updates an assert in the `WindowsPlugin` constructor that
previously crashed because it did not consider `ffiPlugin` unlike
`LinuxPlugin` which does.

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---------

Co-authored-by: Renzo Olivares <roliv@google.com>

Author: Renzo-Olivares

packages/flutter_tools/lib/src/platform_plugins.dart

@@ -441,7 +441,12 @@ class WindowsPlugin extends PluginPlatform implements NativeOrDartPlugin, Varian
     this.defaultPackage,
     this.variants = const <PluginPlatformVariant>{},
   }) : ffiPlugin = ffiPlugin ?? false,
-       assert(pluginClass != null || dartPluginClass != null || defaultPackage != null);
+       assert(
+         pluginClass != null ||
+             dartPluginClass != null ||
+             defaultPackage != null ||
+             (ffiPlugin ?? false),
+       );
 
   factory WindowsPlugin.fromYaml(String name, YamlMap yaml) {
     assert(validate(yaml));