[Prism] Implement defined? for PM_CALL_OPERATOR_WRITE_NODE

Ruby code:

```ruby
defined?(PrismTestSubclass.test_call_operator_write_node += 1)
```

Instructions:

```
"********* Ruby *************"
== disasm: #<ISeq:<compiled>@<compiled>:1 (1,0)-(59,58)>
0000 putobject                              "assignment"              (  59)[Li]
0002 leave
"********* PRISM *************"
== disasm: #<ISeq:<compiled>@<compiled>:58 (58,0)-(58,58)>
0000 putobject                              "assignment"              (  58)[Li]
0002 leave
```

Related: ruby/prism#2188

prism_compile.c

@@ -2687,6 +2687,8 @@ pm_compile_defined_expr0(rb_iseq_t *iseq, const pm_node_t *node, LINK_ANCHOR *co
                   PUSH_VAL(DEFINED_ZSUPER));
         return;
       case PM_CALL_AND_WRITE_NODE:
+      case PM_CALL_OPERATOR_WRITE_NODE:
+
       case PM_CONSTANT_WRITE_NODE:
       case PM_CONSTANT_OPERATOR_WRITE_NODE:
       case PM_CONSTANT_AND_WRITE_NODE:

test/ruby/test_compile_prism.rb

@@ -239,6 +239,7 @@ module Prism
       assert_prism_eval("defined?(`echo #{1}`)")
 
       assert_prism_eval("defined?(PrismTestSubclass.test_call_and_write_node &&= 1)")
+      assert_prism_eval("defined?(PrismTestSubclass.test_call_operator_write_node += 1)")
     end
 
     def test_GlobalVariableReadNode