Add embedder unit test that reproduces https://github.com/dart-lang/sdk/issues/46275 (#27392)

* Add embedder unit test that reproduces the problem described in
https://github.com/dart-lang/sdk/issues/46275

* Address code review comments.

shell/platform/embedder/fixtures/main.dart

@@ -3,12 +3,13 @@
 // found in the LICENSE file.
 
 import 'dart:async';
+import 'dart:convert';
+import 'dart:core';
+import 'dart:ffi';
+import 'dart:io';
+import 'dart:isolate';
 import 'dart:typed_data';
 import 'dart:ui';
-import 'dart:isolate';
-import 'dart:ffi';
-import 'dart:core';
-import 'dart:convert';
 
 void main() {}
 
@@ -32,6 +33,14 @@ void sayHiFromCustomEntrypoint2() native 'SayHiFromCustomEntrypoint2';
 void sayHiFromCustomEntrypoint3() native 'SayHiFromCustomEntrypoint3';
 
 
+@pragma('vm:entry-point')
+void terminateExitCodeHandler() {
+  final ProcessResult result = Process.runSync(
+        'ls', <String>[]
+  );
+}
+
+
 @pragma('vm:entry-point')
 void invokePlatformTaskRunner() {
   PlatformDispatcher.instance.sendPlatformMessage('OhHi', null, null);

shell/platform/embedder/tests/embedder_unittests.cc

@@ -123,6 +123,15 @@ TEST_F(EmbedderTest, CanInvokeCustomEntrypointMacro) {
   ASSERT_TRUE(engine.is_valid());
 }
 
+TEST_F(EmbedderTest, CanTerminateCleanly) {
+  auto& context = GetEmbedderContext(EmbedderTestContextType::kSoftwareContext);
+  EmbedderConfigBuilder builder(context);
+  builder.SetSoftwareRendererConfig();
+  builder.SetDartEntrypoint("terminateExitCodeHandler");
+  auto engine = builder.LaunchEngine();
+  ASSERT_TRUE(engine.is_valid());
+}
+
 std::atomic_size_t EmbedderTestTaskRunner::sEmbedderTaskRunnerIdentifiers = {};
 
 TEST_F(EmbedderTest, CanSpecifyCustomPlatformTaskRunner) {