Refactor parsing object members

[danez]

Q	A
Fixed Issues?
Patch: Bug Fix?	y
Major: Breaking Change?	n
Minor: New Feature?
Tests Added + Pass?	Yes
Documentation PR Link
Any Dependency Changes?
License	MIT

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()

[babel-bot]

Build successful! You can test your changes in the REPL here: https://babeljs.io/repl/build/10340/

[nicolo-ribaudo]

• Parse RestElement in parseObjectMember not with parseRest() as only Identifier is allowed in this context
• Disallow a newline between async and method name.

Could you add some tests for these two points? (Unless I just missed them)

[danez]

I added a test for the async-newline stuff. The RestElement has already tests. It is all the tests that switched from throwing Invalid rest operator's argument to Unexpected token.