Handle nested restrictive annotations on type variables in `@NullUnmarked` code

[msridhar]

import org.jspecify.annotations.NonNull;
import org.jspecify.annotations.NullMarked;
import org.jspecify.annotations.NullUnmarked;
import org.jspecify.annotations.Nullable;

@NullMarked
class Test {

  interface Foo<T extends @Nullable Object> {}

  @NullUnmarked
  static <T> T identity(Foo<@NonNull T> t) {
    throw new RuntimeException("not implemented");
  }

  void test(Foo<@Nullable String> s) {
    String x = identity(s); // we should report an error here
  }
}

Right now we do not report an error at the identity call, but we should, since the restrictive @NonNull annotation in the Foo<@NonNull T> parameter type means you cannot pass Foo<@Nullable String>.