[tool] Update to Dart 3 (#6030)

Updates the repo tooling to Dart 3, now that the N-2 version has Dart 3, which allows us to use Dart 3 features (e.g., records) going forward.

To allow the update:
- Removes `break` commands from `switch`es (all done automatically with `dart fix --apply`)
- Replaces mocking of `ProcessResult` with just creating an actual `ProcessResult` since it's a `final` data class and thus can't (but also doesn't need to be) mocked.

script/tool/test/common/package_command_test.mocks.dart

@@ -1,23 +1,26 @@
-// Mocks generated by Mockito 5.4.0 from annotations
+// Mocks generated by Mockito 5.4.4 from annotations
 // in flutter_plugin_tools/test/common/package_command_test.dart.
 // Do not manually edit this file.
 
 // ignore_for_file: no_leading_underscores_for_library_prefixes
 import 'dart:async' as _i6;
-import 'dart:io' as _i4;
+import 'dart:io' as _i10;
 
 import 'package:git/src/branch_reference.dart' as _i3;
 import 'package:git/src/commit.dart' as _i2;
 import 'package:git/src/commit_reference.dart' as _i8;
-import 'package:git/src/git_dir.dart' as _i5;
+import 'package:git/src/git_dir.dart' as _i4;
 import 'package:git/src/tag.dart' as _i7;
 import 'package:git/src/tree_entry.dart' as _i9;
 import 'package:mockito/mockito.dart' as _i1;
+import 'package:mockito/src/dummies.dart' as _i5;
 
 // ignore_for_file: type=lint
 // ignore_for_file: avoid_redundant_argument_values
 // ignore_for_file: avoid_setters_without_getters
 // ignore_for_file: comment_references
+// ignore_for_file: deprecated_member_use
+// ignore_for_file: deprecated_member_use_from_same_package
 // ignore_for_file: implementation_imports
 // ignore_for_file: invalid_use_of_visible_for_testing_member
 // ignore_for_file: prefer_const_constructors
@@ -46,20 +49,10 @@ class _FakeBranchReference_1 extends _i1.SmartFake
         );
 }
 
-class _FakeProcessResult_2 extends _i1.SmartFake implements _i4.ProcessResult {
-  _FakeProcessResult_2(
-    Object parent,
-    Invocation parentInvocation,
-  ) : super(
-          parent,
-          parentInvocation,
-        );
-}
-
 /// A class which mocks [GitDir].
 ///
 /// See the documentation for Mockito's code generation for more information.
-class MockGitDir extends _i1.Mock implements _i5.GitDir {
+class MockGitDir extends _i1.Mock implements _i4.GitDir {
   MockGitDir() {
     _i1.throwOnMissingStub(this);
   }
@@ -67,8 +60,12 @@ class MockGitDir extends _i1.Mock implements _i5.GitDir {
   @override
   String get path => (super.noSuchMethod(
         Invocation.getter(#path),
-        returnValue: '',
+        returnValue: _i5.dummyValue<String>(
+          this,
+          Invocation.getter(#path),
+        ),
       ) as String);
+
   @override
   _i6.Future<int> commitCount([String? branchName = r'HEAD']) =>
       (super.noSuchMethod(
@@ -78,6 +75,7 @@ class MockGitDir extends _i1.Mock implements _i5.GitDir {
         ),
         returnValue: _i6.Future<int>.value(0),
       ) as _i6.Future<int>);
+
   @override
   _i6.Future<_i2.Commit> commitFromRevision(String? revision) =>
       (super.noSuchMethod(
@@ -93,6 +91,7 @@ class MockGitDir extends _i1.Mock implements _i5.GitDir {
           ),
         )),
       ) as _i6.Future<_i2.Commit>);
+
   @override
   _i6.Future<Map<String, _i2.Commit>> commits([String? branchName = r'HEAD']) =>
       (super.noSuchMethod(
@@ -103,6 +102,7 @@ class MockGitDir extends _i1.Mock implements _i5.GitDir {
         returnValue:
             _i6.Future<Map<String, _i2.Commit>>.value(<String, _i2.Commit>{}),
       ) as _i6.Future<Map<String, _i2.Commit>>);
+
   @override
   _i6.Future<_i3.BranchReference?> branchReference(String? branchName) =>
       (super.noSuchMethod(
@@ -112,6 +112,7 @@ class MockGitDir extends _i1.Mock implements _i5.GitDir {
         ),
         returnValue: _i6.Future<_i3.BranchReference?>.value(),
       ) as _i6.Future<_i3.BranchReference?>);
+
   @override
   _i6.Future<List<_i3.BranchReference>> branches() => (super.noSuchMethod(
         Invocation.method(
@@ -121,6 +122,7 @@ class MockGitDir extends _i1.Mock implements _i5.GitDir {
         returnValue: _i6.Future<List<_i3.BranchReference>>.value(
             <_i3.BranchReference>[]),
       ) as _i6.Future<List<_i3.BranchReference>>);
+
   @override
   _i6.Stream<_i7.Tag> tags() => (super.noSuchMethod(
         Invocation.method(
@@ -129,6 +131,7 @@ class MockGitDir extends _i1.Mock implements _i5.GitDir {
         ),
         returnValue: _i6.Stream<_i7.Tag>.empty(),
       ) as _i6.Stream<_i7.Tag>);
+
   @override
   _i6.Future<List<_i8.CommitReference>> showRef({
     bool? heads = false,
@@ -146,6 +149,7 @@ class MockGitDir extends _i1.Mock implements _i5.GitDir {
         returnValue: _i6.Future<List<_i8.CommitReference>>.value(
             <_i8.CommitReference>[]),
       ) as _i6.Future<List<_i8.CommitReference>>);
+
   @override
   _i6.Future<_i3.BranchReference> currentBranch() => (super.noSuchMethod(
         Invocation.method(
@@ -161,6 +165,7 @@ class MockGitDir extends _i1.Mock implements _i5.GitDir {
           ),
         )),
       ) as _i6.Future<_i3.BranchReference>);
+
   @override
   _i6.Future<List<_i9.TreeEntry>> lsTree(
     String? treeish, {
@@ -178,6 +183,7 @@ class MockGitDir extends _i1.Mock implements _i5.GitDir {
         ),
         returnValue: _i6.Future<List<_i9.TreeEntry>>.value(<_i9.TreeEntry>[]),
       ) as _i6.Future<List<_i9.TreeEntry>>);
+
   @override
   _i6.Future<String?> createOrUpdateBranch(
     String? branchName,
@@ -195,6 +201,7 @@ class MockGitDir extends _i1.Mock implements _i5.GitDir {
         ),
         returnValue: _i6.Future<String?>.value(),
       ) as _i6.Future<String?>);
+
   @override
   _i6.Future<String> commitTree(
     String? treeSha,
@@ -210,8 +217,19 @@ class MockGitDir extends _i1.Mock implements _i5.GitDir {
           ],
           {#parentCommitShas: parentCommitShas},
         ),
-        returnValue: _i6.Future<String>.value(''),
+        returnValue: _i6.Future<String>.value(_i5.dummyValue<String>(
+          this,
+          Invocation.method(
+            #commitTree,
+            [
+              treeSha,
+              commitMessage,
+            ],
+            {#parentCommitShas: parentCommitShas},
+          ),
+        )),
       ) as _i6.Future<String>);
+
   @override
   _i6.Future<Map<String, String>> writeObjects(List<String>? paths) =>
       (super.noSuchMethod(
@@ -221,8 +239,9 @@ class MockGitDir extends _i1.Mock implements _i5.GitDir {
         ),
         returnValue: _i6.Future<Map<String, String>>.value(<String, String>{}),
       ) as _i6.Future<Map<String, String>>);
+
   @override
-  _i6.Future<_i4.ProcessResult> runCommand(
+  _i6.Future<_i10.ProcessResult> runCommand(
     Iterable<String>? args, {
     bool? throwOnError = true,
   }) =>
@@ -232,7 +251,8 @@ class MockGitDir extends _i1.Mock implements _i5.GitDir {
           [args],
           {#throwOnError: throwOnError},
         ),
-        returnValue: _i6.Future<_i4.ProcessResult>.value(_FakeProcessResult_2(
+        returnValue: _i6.Future<_i10.ProcessResult>.value(
+            _i5.dummyValue<_i10.ProcessResult>(
           this,
           Invocation.method(
             #runCommand,
@@ -240,7 +260,8 @@ class MockGitDir extends _i1.Mock implements _i5.GitDir {
             {#throwOnError: throwOnError},
           ),
         )),
-      ) as _i6.Future<_i4.ProcessResult>);
+      ) as _i6.Future<_i10.ProcessResult>);
+
   @override
   _i6.Future<bool> isWorkingTreeClean() => (super.noSuchMethod(
         Invocation.method(
@@ -249,10 +270,11 @@ class MockGitDir extends _i1.Mock implements _i5.GitDir {
         ),
         returnValue: _i6.Future<bool>.value(false),
       ) as _i6.Future<bool>);
+
   @override
   _i6.Future<_i2.Commit?> updateBranch(
     String? branchName,
-    _i6.Future<dynamic> Function(_i4.Directory)? populater,
+    _i6.Future<dynamic> Function(_i10.Directory)? populater,
     String? commitMessage,
   ) =>
       (super.noSuchMethod(
@@ -266,6 +288,7 @@ class MockGitDir extends _i1.Mock implements _i5.GitDir {
         ),
         returnValue: _i6.Future<_i2.Commit?>.value(),
       ) as _i6.Future<_i2.Commit?>);
+
   @override
   _i6.Future<_i2.Commit?> updateBranchWithDirectoryContents(
     String? branchName,