…ed exception in UI isolates on hot restart (flutter/flutter#166064)

…ed exception in UI isolates on hot restart (flutter/flutter#166064)

…ed exception in UI isolates on hot restart (flutter/flutter#166064)

…on in UI isolates on hot restart (flutter#166064)

This pull request is created by [automatic cherry pick workflow](https://github.com/flutter/flutter/blob/main/docs/releases/Flutter-Cherrypick-Process.md#automatically-creates-a-cherry-pick-request)
Please fill in the form below, and a flutter domain expert will evaluate this cherry pick request.

### Issue Link:

flutter#161466

### Changelog Description:

[flutter/161466](flutter#161466): Fixed issue where hot restart could hang indefinitely if "Pause on Unhandled Exceptions" was enabled and a call to `Isolate.run` had not completed.

### Impact Description:

Hot restart (and the Dart-Code extension) could end up in a bad state where hot restart never completes and interacting with the application via the Dart-Code extension doesn't work as expected. The application becomes unresponsive and must be fully restarted to continue development.

`Isolate.run` is used to load license files in the background, meaning that users don't need to explicitly be spawning isolates to encounter this issue.

### Workaround:
Is there a workaround for this issue?

Explicitly disable "Pause on Unhandled Exceptions", which is typically enabled by default.

### Risk:
What is the risk level of this cherry-pick?

### Test Coverage:
Are you confident that your fix is well-tested by automated tests?

### Validation Steps:
What are the steps to validate that this fix works?

1. Create a Flutter project with the following `main.dart`:

```dart

  import 'dart:async';
  import 'dart:developer';
  import 'dart:isolate';

  import 'package:flutter/material.dart';

  void main() {
    WidgetsFlutterBinding.ensureInitialized().platformDispatcher.onError = (Object error, StackTrace? stack) {
      return true;
    };
    runApp(
      const Center(
        child: Text(
          'Hello, world!',
          key: Key('title'),
          textDirection: TextDirection.ltr,
        ),
      ),
    );

    Isolate.run(() {
      print('COMPUTING');
      debugger();
    });
  }
```

2. Run the application in debug mode and perform a hot restart once `COMPUTING` appears on `stdout`. Hot restart should complete successfully.