Print the type name for aggregate values of user-defined types.

[copybara-service]

Print the type name for aggregate values of user-defined types.

For example, say the user defines a fuzz test that takes a struct:

struct Foo {
  int bar = 0;
};

void TakesFoo(Foo foo) {}
FUZZ_TEST(MySuite, TakesFoo)
  .WithDomains(StructOf<Foo>(Arbitrary<int>()));

Previously, the printed value for this looked like {42}, and now it looks
like Foo{42}.