Remove FakeProcessResult for Dart 3 compatibility (#124240)

Removes code that `implements ProcessResult` since it will be `final` in
Dart 3.

Fixes https://github.com/flutter/flutter/issues/124237

## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [ ] All existing and new tests are passing.

packages/fuchsia_remote_debug_protocol/test/src/runners/ssh_command_runner_test.dart

@@ -34,12 +34,10 @@ void main() {
 
   group('SshCommandRunner.run', () {
     late FakeProcessManager fakeProcessManager;
-    late FakeProcessResult fakeProcessResult;
     SshCommandRunner runner;
 
     setUp(() {
-      fakeProcessResult = FakeProcessResult();
-      fakeProcessManager = FakeProcessManager()..fakeResult = fakeProcessResult;
+      fakeProcessManager = FakeProcessManager();
     });
 
     test('verify interface is appended to ipv6 address', () async {
@@ -51,7 +49,7 @@ void main() {
         interface: interface,
         sshConfigPath: '/whatever',
       );
-      fakeProcessResult.stdout = 'somestuff';
+      fakeProcessManager.fakeResult = ProcessResult(23, 0, 'somestuff', null);
             await runner.run('ls /whatever');
       expect(fakeProcessManager.runCommands.single, contains('$ipV6Addr%$interface'));
     });
@@ -62,7 +60,7 @@ void main() {
         fakeProcessManager,
         address: ipV6Addr,
       );
-      fakeProcessResult.stdout = 'somestuff';
+      fakeProcessManager.fakeResult = ProcessResult(23, 0, 'somestuff', null);
       await runner.run('ls /whatever');
       expect(fakeProcessManager.runCommands.single, contains(ipV6Addr));
     });
@@ -71,11 +69,15 @@ void main() {
       const String addr = '192.168.1.1';
       runner = SshCommandRunner.withProcessManager(fakeProcessManager,
           address: addr);
-      fakeProcessResult.stdout = '''
+      fakeProcessManager.fakeResult = ProcessResult(
+          23,
+          0,
+          '''
           this
           has
           four
-          lines''';
+          lines''',
+          null);
       final List<String> result = await runner.run('oihaw');
       expect(result, hasLength(4));
     });
@@ -84,8 +86,7 @@ void main() {
       const String addr = '192.168.1.1';
       runner = SshCommandRunner.withProcessManager(fakeProcessManager,
           address: addr);
-      fakeProcessResult.stdout = 'whatever';
-      fakeProcessResult.exitCode = 1;
+      fakeProcessManager.fakeResult = ProcessResult(23, 1, 'whatever', null);
       Future<void> failingFunction() async {
         await runner.run('oihaw');
       }
@@ -101,7 +102,7 @@ void main() {
         address: addr,
         sshConfigPath: config,
       );
-      fakeProcessResult.stdout = 'somestuff';
+      fakeProcessManager.fakeResult = ProcessResult(23, 0, 'somestuff', null);
       await runner.run('ls /whatever');
       final List<String?> passedCommand = fakeProcessManager.runCommands.single as List<String?>;
       expect(passedCommand, contains('-F'));
@@ -116,7 +117,7 @@ void main() {
         fakeProcessManager,
         address: addr,
       );
-      fakeProcessResult.stdout = 'somestuff';
+      fakeProcessManager.fakeResult = ProcessResult(23, 0, 'somestuff', null);
       await runner.run('ls /whatever');
       final List<String?> passedCommand = fakeProcessManager.runCommands.single as List<String?>;
       final int indexOfFlag = passedCommand.indexOf('-F');
@@ -126,7 +127,7 @@ void main() {
 }
 
 class FakeProcessManager extends Fake implements ProcessManager {
-  FakeProcessResult? fakeResult;
+  ProcessResult? fakeResult;
 
   List<List<dynamic>> runCommands = <List<dynamic>>[];
 
@@ -143,14 +144,3 @@ class FakeProcessManager extends Fake implements ProcessManager {
     return fakeResult!;
   }
 }
-
-class FakeProcessResult extends Fake implements ProcessResult {
-  @override
-  int exitCode = 0;
-
-  @override
-  dynamic stdout;
-
-  @override
-  dynamic stderr;
-}