This makes some changes around destructuring, restspread and objects.

• Split the actual parsing of object-members from parseObj()-loop into parseObjectMember.
• Parse RestElement in parseObjectMember not with parseSpread() + toAssignable() as that seems an overkill if we can parse it directly.
• Parse RestElement in parseObjectMember not with parseRest() as only Identifier is allowed in this context
• Do allow object shorthand property duplicates named __proto__. The spec specifically says only duplicates which come from the form *PropertyDefinition: PropertyName : AssignmentExpression* : https://www.ecma-international.org/ecma-262/9.0/index.html#sec-__proto__-property-names-in-object-initializers
• Disallow a newline between async and method name.
• Refactored the trailing comma after rest element messages. We had lots of different variations for this error and I opted to go for one message for all cases (same as chrome): "Rest element must be last element" This makes the code a little bit simpler
• Rename parseRest() to parseRestBinding()