docImports for the widgets library (#152339)

https://github.com/flutter/flutter/issues/150800. The 2nd batch of `widgets` library `@docImport`s.

After this patch, in the `widgets` library:
```
Can not fully resolve ../../flutter/packages/flutter/lib/src/widgets/scroll_view.dart: (TargetPlatformVariant.mobile)
Can not fully resolve ../../flutter/packages/flutter/lib/src/widgets/_platform_selectable_region_context_menu_web.dart: (ui_web.platformViewRegistry.registerViewFactory)
Can not fully resolve ../../flutter/packages/flutter/lib/src/widgets/primary_scroll_controller.dart: (TargetPlatformVariant.mobile)
Can not fully resolve ../../flutter/packages/flutter/lib/src/widgets/selectable_region.dart: (material, WidgetTester.dragFrom)
Can not fully resolve ../../flutter/packages/flutter/lib/src/widgets/basic.dart: (ui.Gradient.linear)
Can not fully resolve ../../flutter/packages/flutter/lib/src/widgets/framework.dart: (Finder)
Can not fully resolve ../../flutter/packages/flutter/lib/src/widgets/draggable_scrollable_sheet.dart: (WidgetTester.pumpAndSettle)
Can not fully resolve ../../flutter/packages/flutter/lib/src/widgets/binding.dart: (WidgetTester.restartAndRestore, WidgetTester.pumpWidget, TestWidgetsFlutterBinding, testWidgets, TestWidgetsFlutterBinding.ensureInitialized)
Can not fully resolve ../../flutter/packages/flutter/lib/src/widgets/localizations.dart: (GlobalWidgetsLocalizations)
Can not fully resolve ../../flutter/packages/flutter/lib/src/widgets/scroll_controller.dart: (WidgetTester.pumpAndSettle)
Can not fully resolve ../../flutter/packages/flutter/lib/src/widgets/scrollbar.dart: (TargetPlatformVariant.desktop)
21 out-of-scope references in 11 files, 16 unique symbols were left unresolved.
```

packages/flutter/lib/src/widgets/app.dart

@@ -665,7 +665,7 @@ class WidgetsApp extends StatefulWidget {
   ///
   /// When a named route is pushed with [Navigator.pushNamed], the route name is
   /// looked up in this map. If the name is present, the associated
-  /// [widgets.WidgetBuilder] is used to construct a [PageRoute] specified by
+  /// [WidgetBuilder] is used to construct a [PageRoute] specified by
   /// [pageRouteBuilder] to perform an appropriate transition, including [Hero]
   /// animations, to the new route.
   ///
@@ -1359,7 +1359,7 @@ class _WidgetsAppState extends State<WidgetsApp> with WidgetsBindingObserver {
 
   AppLifecycleState? _appLifecycleState;
 
-  /// The default value for [onNavigationNotification].
+  /// The default value for [WidgetsApp.onNavigationNotification].
   ///
   /// Does nothing and stops bubbling if the app is detached. Otherwise, updates
   /// the platform with [NavigationNotification.canHandlePop] and stops

packages/flutter/lib/src/widgets/draggable_scrollable_sheet.dart

@@ -1071,7 +1071,7 @@ class _DraggableScrollableActuatorState extends State<DraggableScrollableActuato
   }
 }
 
-/// A [ChangeNotifier] to use with [InheritedResetNotifier] to notify
+/// A [ChangeNotifier] to use with [_InheritedResetNotifier] to notify
 /// descendants that they should reset to initial state.
 class _ResetNotifier extends ChangeNotifier {
   _ResetNotifier() {

packages/flutter/lib/src/widgets/editable_text.dart

@@ -5096,7 +5096,7 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
   }
 
 
-  /// The default behavior used if [onTapOutside] is null.
+  /// The default behavior used if [EditableText.onTapOutside] is null.
   ///
   /// The `event` argument is the [PointerDownEvent] that caused the notification.
   void _defaultOnTapOutside(PointerDownEvent event) {
@@ -5748,7 +5748,7 @@ class _ScribblePlaceholder extends WidgetSpan {
 /// See also:
 ///
 ///  * [String.runes], which deals with code points like this class.
-///  * [String.characters], which deals with graphemes.
+///  * [Characters], which deals with graphemes.
 ///  * [CharacterBoundary], which is a [TextBoundary] like this class, but whose
 ///    boundaries are graphemes instead of code points.
 class _CodePointBoundary extends TextBoundary {

packages/flutter/lib/src/widgets/framework.dart

@@ -2651,8 +2651,8 @@ final class BuildScope {
   ///
   /// This is necessary to preserve the sort order defined by [Element._sort].
   ///
-  /// This field is set to null when [buildScope] is not actively rebuilding
-  /// the widget tree.
+  /// This field is set to null when [BuildOwner.buildScope] is not actively
+  /// rebuilding the widget tree.
   bool? _dirtyElementsNeedsResorting;
   final List<Element> _dirtyElements = <Element>[];
 

packages/flutter/lib/src/widgets/modal_barrier.dart

@@ -31,7 +31,7 @@ import 'transitions.dart';
 ///  * [ModalBarrier], which utilizes this widget to adjust the barrier focus
 /// size based on the size of the content layer rendered on top of it.
 class _SemanticsClipper extends SingleChildRenderObjectWidget{
-  /// creates a [SemanticsClipper] that updates the size of the
+  /// creates a [_SemanticsClipper] that updates the size of the
   /// [SemanticsNode.rect] of its child based on the value inside the provided
   /// [ValueNotifier], or a default value of [EdgeInsets.zero].
   const _SemanticsClipper({

packages/flutter/lib/src/widgets/service_extensions.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+/// @docImport 'dart:developer';
 /// @docImport 'package:flutter/foundation.dart';
 /// @docImport 'package:flutter/rendering.dart';
 ///

packages/flutter/lib/src/widgets/widget_inspector.dart

@@ -2,6 +2,9 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+/// @docImport 'dart:ui';
+library;
+
 import 'dart:async';
 import 'dart:collection' show HashMap;
 import 'dart:convert';
@@ -543,11 +546,11 @@ class _ScreenshotPaintingContext extends PaintingContext {
   /// size of [renderBounds] multiplied by [pixelRatio].
   ///
   /// To use [toImage], the render object must have gone through the paint phase
-  /// (i.e. [debugNeedsPaint] must be false).
+  /// (i.e. [RenderObject.debugNeedsPaint] must be false).
   ///
   /// The [pixelRatio] describes the scale between the logical pixels and the
   /// size of the output image. It is independent of the
-  /// [window.devicePixelRatio] for the device, so specifying 1.0 (the default)
+  /// [FlutterView.devicePixelRatio] for the device, so specifying 1.0 (the default)
   /// will give you a 1:1 mapping between logical pixels and the output pixels
   /// in the image.
   ///
@@ -917,7 +920,7 @@ mixin WidgetInspectorService {
   /// `value` reflects the newly updated service extension value.
   ///
   /// This will be called automatically for service extensions registered via
-  /// [registerBoolServiceExtension].
+  /// [BindingBase.registerBoolServiceExtension].
   void _postExtensionStateChangedEvent(String name, Object? value) {
     postEvent(
       'Flutter.ServiceExtensionStateChanged',