Add previews for CupertinoIcons (#71853)

dev/docs/assets/overrides.css

@@ -146,3 +146,8 @@ footer {
   font-style: italic;
   font-weight: bold;
 }
+
+/* Constrain image width to container */
+img {
+  max-width: 100%
+}

dev/docs/styles.html

@@ -4,6 +4,8 @@
 @import 'https://fonts.googleapis.com/css?family=Material+Icons|Material+Icons+Outlined|Material+Icons+Sharp|Material+Icons+Round';
 </style>
 
+<link href="https://flutter.github.io/cupertino_icons/css/icons.css" rel="stylesheet" type="text/css">
+
 <link href="../assets/overrides.css" rel="stylesheet" type="text/css">
 
 <link href="https://fonts.googleapis.com/icon?family=Material+Icons|Material+Icons+Outlined|Material+Icons+Sharp|Material+Icons+Round" rel="stylesheet">

packages/flutter/lib/src/material/icons.dart

@@ -130,7 +130,7 @@ class _PlatformAdaptiveIcons {
 ///
 ///  * [Icon]
 ///  * [IconButton]
-///  * <https://design.google.com/icons/>
+///  * <https://material.io/resources/icons>
 class Icons {
   // This class is not meant to be instantiated or extended; this constructor
   // prevents instantiation and extension.