Fix nullability for some routing related stuff (#67675)

packages/flutter/lib/src/rendering/layer.dart

@@ -2225,7 +2225,7 @@ class FollowerLayer extends ContainerLayer {
   Matrix4? _invertedTransform;
   bool _inverseDirty = true;
 
-  Offset? _transformOffset<S extends Object>(Offset localPosition) {
+  Offset? _transformOffset(Offset localPosition) {
     if (_inverseDirty) {
       _invertedTransform = Matrix4.tryInvert(getLastTransform()!);
       _inverseDirty = false;
@@ -2245,7 +2245,7 @@ class FollowerLayer extends ContainerLayer {
       }
       return false;
     }
-    final Offset? transformedOffset = _transformOffset<S>(localPosition);
+    final Offset? transformedOffset = _transformOffset(localPosition);
     if (transformedOffset == null) {
       return false;
     }

packages/flutter/lib/src/services/raw_keyboard.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-
 import 'dart:io';
 import 'dart:ui';
 
@@ -737,7 +736,7 @@ class RawKeyboard {
 }
 
 @immutable
-class _ModifierSidePair extends Object {
+class _ModifierSidePair {
   const _ModifierSidePair(this.modifier, this.side);
 
   final ModifierKey modifier;

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

@@ -131,7 +131,6 @@ class Draggable<T extends Object> extends StatefulWidget {
        assert(maxSimultaneousDrags == null || maxSimultaneousDrags >= 0),
        super(key: key);
 
-
   /// The data that will be dropped by this draggable.
   final T? data;
 

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

@@ -881,7 +881,7 @@ abstract class ModalRoute<T> extends TransitionRoute<T> with LocalHistoryRoute<T
   /// The given [BuildContext] will be rebuilt if the state of the route changes
   /// while it is visible (specifically, if [isCurrent] or [canPop] change value).
   @optionalTypeArgs
-  static ModalRoute<T>? of<T extends Object>(BuildContext context) {
+  static ModalRoute<T>? of<T extends Object?>(BuildContext context) {
     final _ModalScopeStatus? widget = context.dependOnInheritedWidgetOfExactType<_ModalScopeStatus>();
     return widget?.route as ModalRoute<T>?;
   }
@@ -1818,7 +1818,7 @@ class _DialogRoute<T> extends PopupRoute<T> {
 ///
 ///  * [showDialog], which displays a Material-style dialog.
 ///  * [showCupertinoDialog], which displays an iOS-style dialog.
-Future<T> showGeneralDialog<T extends Object>({
+Future<T> showGeneralDialog<T extends Object?>({
   required BuildContext context,
   required RoutePageBuilder pageBuilder,
   bool barrierDismissible = false,