Add missing HIG links to cupertino documentation (#103110)

packages/flutter/lib/src/cupertino/bottom_tab_bar.dart

@@ -55,6 +55,7 @@ const Color _kDefaultTabBarInactiveColor = CupertinoColors.inactiveGray;
 ///
 ///  * [CupertinoTabScaffold], which hosts the [CupertinoTabBar] at the bottom.
 ///  * [BottomNavigationBarItem], an item in a [CupertinoTabBar].
+///  * <https://developer.apple.com/design/human-interface-guidelines/ios/bars/tab-bars/>
 class CupertinoTabBar extends StatelessWidget implements PreferredSizeWidget {
   /// Creates a tab bar in the iOS style.
   const CupertinoTabBar({

packages/flutter/lib/src/cupertino/context_menu.dart

@@ -91,7 +91,7 @@ enum _ContextMenuLocation {
 ///
 /// See also:
 ///
-///  * [Apple's HIG for Context Menus](https://developer.apple.com/design/human-interface-guidelines/ios/controls/context-menus/)
+///  * <https://developer.apple.com/design/human-interface-guidelines/ios/controls/context-menus/>
 class CupertinoContextMenu extends StatefulWidget {
   /// Create a context menu.
   ///

packages/flutter/lib/src/cupertino/date_picker.dart

@@ -218,6 +218,7 @@ enum _PickerColumnType {
 ///
 ///  * [CupertinoTimerPicker], the class that implements the iOS-style timer picker.
 ///  * [CupertinoPicker], the class that implements a content agnostic spinner UI.
+///  * <https://developer.apple.com/design/human-interface-guidelines/ios/controls/pickers/>
 class CupertinoDatePicker extends StatefulWidget {
   /// Constructs an iOS style date picker.
   ///
@@ -1508,6 +1509,7 @@ enum CupertinoTimerPickerMode {
 ///  * [CupertinoDatePicker], the class that implements different display modes
 ///    of the iOS-style date picker.
 ///  * [CupertinoPicker], the class that implements a content agnostic spinner UI.
+///  * <https://developer.apple.com/design/human-interface-guidelines/ios/controls/pickers/>
 class CupertinoTimerPicker extends StatefulWidget {
   /// Constructs an iOS style countdown timer picker.
   ///

packages/flutter/lib/src/cupertino/nav_bar.dart

@@ -237,6 +237,7 @@ bool _isTransitionable(BuildContext context) {
 ///    [CupertinoNavigationBar].
 ///  * [CupertinoSliverNavigationBar] for a navigation bar to be placed in a
 ///    scrolling list and that supports iOS-11-style large titles.
+///  * <https://developer.apple.com/design/human-interface-guidelines/ios/bars/navigation-bars/>
 class CupertinoNavigationBar extends StatefulWidget implements ObstructingPreferredSizeWidget {
   /// Creates a navigation bar in the iOS style.
   const CupertinoNavigationBar({
@@ -573,6 +574,7 @@ class _CupertinoNavigationBarState extends State<CupertinoNavigationBar> {
 ///  * [CupertinoNavigationBar], an iOS navigation bar for use on non-scrolling
 ///    pages.
 ///  * [CustomScrollView], a ScrollView that creates custom scroll effects using slivers.
+///  * <https://developer.apple.com/design/human-interface-guidelines/ios/bars/navigation-bars/>
 class CupertinoSliverNavigationBar extends StatefulWidget {
   /// Creates a navigation bar for scrolling lists.
   ///

packages/flutter/lib/src/cupertino/search_field.dart

@@ -39,6 +39,9 @@ import 'text_field.dart';
 /// ** See code in examples/api/lib/cupertino/search_field/cupertino_search_field.1.dart **
 /// {@end-tool}
 ///
+/// See also:
+///
+///  * <https://developer.apple.com/design/human-interface-guidelines/ios/bars/search-bars/>
 class CupertinoSearchTextField extends StatefulWidget {
   /// Creates a [CupertinoTextField] that mimics the look and behavior of
   /// UIKit's `UISearchTextField`.

packages/flutter/lib/src/cupertino/text_field.dart

@@ -168,6 +168,7 @@ class _CupertinoTextFieldSelectionGestureDetectorBuilder extends TextSelectionGe
 ///  * [EditableText], which is the raw text editing control at the heart of a
 ///    [TextField].
 ///  * Learn how to use a [TextEditingController] in one of our [cookbook recipes](https://flutter.dev/docs/cookbook/forms/text-field-changes#2-use-a-texteditingcontroller).
+///  * <https://developer.apple.com/design/human-interface-guidelines/ios/controls/text-fields/>
 class CupertinoTextField extends StatefulWidget {
   /// Creates an iOS-style text field.
   ///