[vm/ffi] Mark dart:ffi as stable

Closes: #34452

We will still actively adding new features to `dart:ffi`. Please refer
to https://github.com/dart-lang/sdk/labels/library-ffi for open issues
and feature requests.

Related documentation PRs:
- dart-lang/site-www#2873
- flutter/website#5195

Change-Id: I59a23e462c859da5dcd2e5548fb6fe295c5d8532
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/179765
Commit-Queue: Daco Harkes <[email protected]>
Reviewed-by: Michael Thomsen <[email protected]>

Author: dcharkes

sdk/lib/_internal/sdk_library_metadata/lib/libraries.dart

@@ -64,10 +64,7 @@ const Map<String, LibraryInfo> libraries = const {
       maturity: Maturity.UNSTABLE,
       dart2jsPatchPath: "_internal/js_runtime/lib/developer_patch.dart"),
   "ffi": const LibraryInfo("ffi/ffi.dart",
-      categories: "Server",
-      // TODO(dacoharkes): Update maturity when we release dart:ffi.
-      // https://github.com/dart-lang/sdk/issues/34452
-      maturity: Maturity.EXPERIMENTAL),
+      categories: "Server", maturity: Maturity.STABLE),
   "html": const LibraryInfo("html/dart2js/html_dart2js.dart",
       categories: "Client",
       maturity: Maturity.WEB_STABLE,

sdk/lib/ffi/ffi.dart

@@ -5,8 +5,6 @@
 /**
  * Foreign Function Interface for interoperability with the C programming language.
  *
- * **NOTE**: Dart:FFI is in beta, and breaking API changes might still happen.
- *
  * For further details, please see: https://dart.dev/server/c-interop
  *
  * {@category VM}