Move mock canvas to flutter_test (#131631)

Fixes #59413

This relocates `mock_canvas.dart` and `recording_canvas.dart` from `flutter/test/rendering` to `flutter_test`. 

The testing functionality afforded by mock_canvas should be available to everyone, not just the framework. :)

mock_canvas.dart needed a bit of cleanup - things like formatting and super parameters.

Author: Piinks

packages/flutter/test/cupertino/activity_indicator_test.dart

@@ -11,8 +11,6 @@ import 'package:flutter/cupertino.dart';
 import 'package:flutter/scheduler.dart';
 import 'package:flutter_test/flutter_test.dart';
 
-import '../rendering/mock_canvas.dart';
-
 void main() {
   testWidgets('Activity indicator animate property works', (WidgetTester tester) async {
     await tester.pumpWidget(buildCupertinoActivityIndicator());

packages/flutter/test/cupertino/checkbox_test.dart

@@ -8,7 +8,6 @@ import 'package:flutter/rendering.dart';
 import 'package:flutter/services.dart';
 import 'package:flutter_test/flutter_test.dart';
 
-import '../rendering/mock_canvas.dart';
 import '../widgets/semantics_tester.dart';
 
 void main() {

packages/flutter/test/cupertino/colors_test.dart

@@ -6,8 +6,6 @@ import 'package:flutter/cupertino.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
 
-import '../rendering/mock_canvas.dart';
-
 class DependentWidget extends StatelessWidget {
   const DependentWidget({
     super.key,

packages/flutter/test/cupertino/context_menu_action_test.dart

@@ -8,8 +8,6 @@ import 'package:flutter/gestures.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter_test/flutter_test.dart';
 
-import '../rendering/mock_canvas.dart';
-
 void main() {
   // Constants taken from _ContextMenuActionState.
   const CupertinoDynamicColor kBackgroundColor =

packages/flutter/test/cupertino/dialog_test.dart

@@ -16,7 +16,6 @@ import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter_test/flutter_test.dart';
 
-import '../rendering/mock_canvas.dart';
 import '../widgets/semantics_tester.dart';
 
 void main() {

packages/flutter/test/cupertino/nav_bar_test.dart

@@ -12,7 +12,6 @@ import 'package:flutter/rendering.dart';
 import 'package:flutter/services.dart';
 import 'package:flutter_test/flutter_test.dart';
 
-import '../rendering/mock_canvas.dart';
 import '../widgets/semantics_tester.dart';
 
 int count = 0;

packages/flutter/test/cupertino/picker_test.dart

@@ -9,7 +9,6 @@ import 'package:flutter/rendering.dart';
 import 'package:flutter/services.dart';
 import 'package:flutter_test/flutter_test.dart';
 
-import '../rendering/mock_canvas.dart';
 import '../rendering/rendering_tester.dart';
 
 class SpyFixedExtentScrollController extends FixedExtentScrollController {

packages/flutter/test/cupertino/radio_test.dart

@@ -8,7 +8,6 @@ import 'package:flutter/rendering.dart';
 import 'package:flutter/services.dart';
 import 'package:flutter_test/flutter_test.dart';
 
-import '../rendering/mock_canvas.dart';
 import '../widgets/semantics_tester.dart';
 
 void main() {

packages/flutter/test/cupertino/route_test.dart

@@ -13,7 +13,6 @@ import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter_test/flutter_test.dart';
 
-import '../rendering/mock_canvas.dart';
 import '../widgets/semantics_tester.dart';
 
 void main() {

packages/flutter/test/cupertino/scaffold_test.dart

@@ -8,7 +8,6 @@ import 'package:flutter/cupertino.dart';
 import 'package:flutter_test/flutter_test.dart';
 
 import '../image_data.dart';
-import '../rendering/mock_canvas.dart';
 
 /// Integration tests testing both [CupertinoPageScaffold] and [CupertinoTabScaffold].
 void main() {