Using `..` for Open Record Patterns/Destructuring

[smores56]

We want to start using the below syntax for open/constrained records:

{ a, b, .. } = data

and the following for closed records:

{ a, b } = data

This facilitates Roc devs being able to define closed records that will raise type errors if the destructured values get additional fields added. This is not possible in Roc today.

This change will probably break a good deal of existing Roc code that assumes that { a, b } destructures are open records, but the direction of this change precludes the ability to facilitate the transition with smart parsing + formatting.

[mitulagr2]

I'll take this if you'd like!

[smores56]

@mitulagr2 great! I've assigned it to you and thrown on the "Hacktoberfest" label. Let me know here or on the Zulip if you have any questions.