Out of experimental

We can mark ourselves as no longer experimental.
diff --git a/pubspec.yaml b/pubspec.yaml
index ee8544d..e9d7f66 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -5,7 +5,7 @@
 name: ffigen
 version: 2.0.0
 homepage: https://github.com/dart-lang/ffigen
-description: Experimental generator for FFI bindings, using LibClang to parse C header files.
+description: Generator for FFI bindings, using LibClang to parse C header files.
 
 environment:
   sdk: '>=2.12.0-259.9.beta <3.0.0'