Raise error on take/send for Ractors in child processes

Ractor objects that are available in a child process should raise a
`Ractor::ClosedError` exception when called with `send` or `take`

Co-authored-by: John Hawthorn <john@hawthorn.email>

bootstraptest/test_ractor.rb

@@ -2213,7 +2213,49 @@ assert_equal 'ok', %q{
 
 # fork after creating Ractor
 assert_equal 'ok', %q{
+begin
   Ractor.new { Ractor.receive }
   _, status = Process.waitpid2 fork { }
   status.success? ? "ok" : status
+rescue NotImplementedError
+  :ok
+end
+}
+
+# Ractors should be terminated after fork
+assert_equal 'ok', %q{
+begin
+  r = Ractor.new { Ractor.receive }
+  _, status = Process.waitpid2 fork {
+    begin
+      r.take
+      raise "ng"
+    rescue Ractor::ClosedError
+    end
+  }
+  r.send(123)
+  raise unless r.take == 123
+  status.success? ? "ok" : status
+rescue NotImplementedError
+  :ok
+end
+}
+
+# Ractors should be terminated after fork
+assert_equal 'ok', %q{
+begin
+  r = Ractor.new { Ractor.receive }
+  _, status = Process.waitpid2 fork {
+    begin
+      r.send(123)
+      raise "ng"
+    rescue Ractor::ClosedError
+    end
+  }
+  r.send(123)
+  raise unless r.take == 123
+  status.success? ? "ok" : status
+rescue NotImplementedError
+  :ok
+end
 }

ractor.c

@@ -2096,6 +2096,9 @@ rb_ractor_terminate_atfork(rb_vm_t *vm, rb_ractor_t *r)
     rb_gc_ractor_cache_free(r->newobj_cache);
     r->newobj_cache = NULL;
     r->status_ = ractor_terminated;
+    r->sync.outgoing_port_closed = true;
+    r->sync.incoming_port_closed = true;
+    r->sync.will_basket.type.e = basket_type_none;
 }
 #endif