[pkg:js] Clarify and improve discontinue message

Add library-level docs duplicating the discontinue message

Related to #59716

Change-Id: Ib414a56c4412db0d9701c3d11f75354295775f9b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/408642
Commit-Queue: Srujan Gaddam <[email protected]>
Reviewed-by: Srujan Gaddam <[email protected]>
Auto-Submit: Kevin Moore <[email protected]>

Author: kevmoo

pkg/js/README.md

@@ -2,9 +2,11 @@
 [![package publisher](https://img.shields.io/pub/publisher/js.svg)](https://pub.dev/packages/js/publisher)
 
 > [!CAUTION]
-> This package is discontinued.
-> Prefer using `dart:js_interop` instead of this package for JS 
-> interop. See the [JS interop documentation] for more details.
+> This package is discontinued. Prefer using
+> [`dart:js_interop`](https://api.dart.dev/dart-js_interop/dart-js_interop-library.html)
+> for JS interop. See the
+> [JS interop documentation](https://dart.dev/interop/js-interop) for more
+> details.
 
 Use this package when you want to call JavaScript APIs from Dart code, or vice
 versa.

pkg/js/lib/js.dart

@@ -2,6 +2,12 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+/// > [!CAUTION]
+/// > This package is discontinued. Prefer using
+/// > [`dart:js_interop`](https://api.dart.dev/dart-js_interop/dart-js_interop-library.html)
+/// > for JS interop. See the
+/// > [JS interop documentation](https://dart.dev/interop/js-interop) for more
+/// > details.
 @Deprecated('Use dart:js_interop instead')
 library;
 

pkg/js/lib/js_util.dart

@@ -3,6 +3,13 @@
 // BSD-style license that can be found in the LICENSE file.
 
 /// Utilities for interoperating with JavaScript.
+///
+/// > [!CAUTION]
+/// > This package is discontinued. Prefer using
+/// > [`dart:js_interop`](https://api.dart.dev/dart-js_interop/dart-js_interop-library.html)
+/// > for JS interop. See the
+/// > [JS interop documentation](https://dart.dev/interop/js-interop) for more
+/// > details.
 @Deprecated('Use dart:js_interop instead')
 library;