Duplicate PropertyName of `__proto__` should be accepted in destructuring

[KFlash]

Annex B defines an early error for duplicate PropertyName of __proto__, in object initializers, but this does not apply to Object Assignment patterns

Steps to reproduce

esprima.parse('result = { __proto__: x, __proto__: y } = value;')

// Parenthesized
esprima.parse('result = ({ __proto__: x, __proto__: y } = value);')

Expected output

{
    "type": "Program",
    "body": [
        {
            "type": "ExpressionStatement",
            "expression": {
                "type": "AssignmentExpression",
                "left": {
                    "type": "Identifier",
                    "name": "result"
                },
                "operator": "=",
                "right": {
                    "type": "AssignmentExpression",
                    "left": {
                        "type": "ObjectPattern",
                        "properties": [
                            {
                                "type": "Property",
                                "key": {
                                    "type": "Identifier",
                                    "name": "__proto__"
                                },
                                "value": {
                                    "type": "Identifier",
                                    "name": "x"
                                },
                                "kind": "init",
                                "computed": false,
                                "method": false,
                                "shorthand": false
                            },
                            {
                                "type": "Property",
                                "key": {
                                    "type": "Identifier",
                                    "name": "__proto__"
                                },
                                "value": {
                                    "type": "Identifier",
                                    "name": "y"
                                },
                                "kind": "init",
                                "computed": false,
                                "method": false,
                                "shorthand": false
                            }
                        ]
                    },
                    "operator": "=",
                    "right": {
                        "type": "Identifier",
                        "name": "value"
                    }
                }
            }
        }
    ],
    "sourceType": "script"
}

Actual output

Throws Error: Line 1: Duplicate __proto__ fields are not allowed in object literals

Relevant references

There exist an Test262 test for this