Add new FFI test source to Fuchsia test package.

Change-Id: I6fea0a683731e8de865c952d1404e468774b3a02
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/410744
Reviewed-by: Alexander Aprelev <[email protected]>
Commit-Queue: Ryan Macnak <[email protected]>

Author: rmacnak-google

BUILD.gn

@@ -358,6 +358,7 @@ if (is_fuchsia) {
     "tests/ffi/structs_typed_data_test.dart",
     "tests/ffi/unaligned_test.dart",
     "tests/ffi/variance_function_test.dart",
+    "tests/ffi/vmspecific_callback_unwind_error_through_handle_test.dart",
     "tests/ffi/vmspecific_deprecated_funcs_test.dart",
     "tests/ffi/vmspecific_dynamic_library_test.dart",
     "tests/ffi/vmspecific_enable_ffi_test.dart",