support trailing commas for object rest

[graingert]

# support trailing commas when the last property is a rest.
const {
    a,
    ...b,
} = foo;

# maybe worth adding for arrays too?
const [
    c,
    ...d,
] = bar;

[loganfsmyth]

This is already allowed in the spec. Trailing commas are only disallowed for object rest, not object spread, which is consistent with the behavior for arrays.

[graingert]

@loganfsmyth updated

[loganfsmyth]

The trailing comma implies that there could be more stuff after it, but since it is a rest, there cannot be, which is why the comma isn't allowed for arrays either.