[tests/ffi] Folder deletion on Windows

On windows we do have a crashpad handler we use to capture coredumps.
This functionality is initialized in `runtime/bin/main_impl.cc` /
`runtime/bin/crashpad.cc`. That may start a subprocess. If that
subprocess has the tempdir as working directory (or inherit handles
referring to it / subdirs/subfiles) it may prevent it from being
deleted.
Adding '--suppress-core-dump' to the Dart process invocations prevents
this.

TEST=ffi/native_assets/infer_native_assets_yaml_dart_kernel_snapshot
TEST=ffi/native_assets/infer_native_assets_yaml_process_run

Closes: https://github.com/dart-lang/sdk/issues/51067

Change-Id: I75807e65e9911653983158a238194968aaedb51f
Cq-Include-Trybots: luci.dart.try:vm-kernel-nnbd-win-debug-x64-try,vm-kernel-nnbd-win-release-ia32-try,vm-kernel-nnbd-win-release-x64-try,vm-kernel-precomp-nnbd-win-release-x64-try
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/279399
Commit-Queue: Daco Harkes <dacoharkes@google.com>
Reviewed-by: Martin Kustermann <kustermann@google.com>

tests/ffi/analysis_options.yaml

@@ -4,3 +4,7 @@ analyzer:
 
   enable-experiment:
     - records # TODO(http://dartbug.com/50586): Remove this when records are no longer an experiment.
+
+linter:
+  rules:
+    - unawaited_futures

tests/ffi/native_assets/asset_executable_test.dart

@@ -59,7 +59,7 @@ Future<void> selfInvokes() async {
 }
 
 Future<void> runTests() async {
-  testExecutable();
+  await testExecutable();
   testNonExistingFunction();
 }
 

tests/ffi/native_assets/helpers.dart

@@ -72,13 +72,13 @@ Future<void> withTempDir(
   Future<void> fun(Uri tempUri), {
   String prefix = 'tests_ffi_native_assets_',
 }) async {
-  final tempDir = Directory.systemTemp.createTempSync(prefix);
+  final tempDir = await Directory.systemTemp.createTemp(prefix);
   try {
     await fun(tempDir.uri);
   } finally {
     if (!Platform.environment.containsKey(keepTempKey) ||
         Platform.environment[keepTempKey]!.isEmpty) {
-      tempDir.deleteSync(recursive: true);
+      await tempDir.delete(recursive: true);
     }
   }
 }
@@ -123,7 +123,7 @@ Future<void> runGenKernel({
   required Uri outputUri,
   Uri? inputUri,
   Uri? nativeAssetsUri,
-}) async =>
+}) =>
     runProcess(
       executable: genKernelUri.toFilePath(),
       arguments: [
@@ -148,14 +148,13 @@ Future<void> createDillFile({
   required Uri dartProgramUri,
   required Uri nativeAssetsUri,
   required Runtime runtime,
-}) async {
-  await runGenKernel(
-    runtime: runtime,
-    outputUri: outputUri,
-    inputUri: dartProgramUri,
-    nativeAssetsUri: nativeAssetsUri,
-  );
-}
+}) =>
+    runGenKernel(
+      runtime: runtime,
+      outputUri: outputUri,
+      inputUri: dartProgramUri,
+      nativeAssetsUri: nativeAssetsUri,
+    );
 
 Future<void> runGenSnapshot({
   required Uri dillUri,
@@ -180,6 +179,8 @@ Future<void> runDart({
     runProcess(
       executable: dartUri.toFilePath(),
       arguments: [
+        // Prevent subprocesses holding on to [workingDirectory] on Windows.
+        '--suppress-core-dump',
         ...toolArgs,
         if (packageConfigUri != null)
           '--packages=${packageConfigUri.toFilePath()}',
@@ -194,7 +195,7 @@ Future<void> runDartKernelSnapshot({
   required Uri inputUri,
   Uri? packageConfigUri,
   Uri? workingDirectory,
-}) async =>
+}) =>
     runDart(
       workingDirectory: workingDirectory,
       toolArgs: [