Supporting of new Set methods in observable Sets

[inoyakaigor]

Intended outcome:
According to a New Set methods proposal a Set class will have a bunch of new methods (more on MDN). This proposal currently at Stage 3 therefore it means it is becoming part of ECMAScript standart

Current browser's support

Method	Firefox (Nigthly)	Chrome (> 122)	Safari (> 17)
intersection	⏳	✔️	✔️
union	⏳	✔️	✔️
difference	⏳	✔️	✔️
symmetricDifference	⏳	✔️	✔️
isSubsetOf	⏳	✔️	✔️
isSupersetOf	⏳	✔️	✔️
isDisjointFrom	⏳	✔️	✔️

I've created a sandbox with example of code that includes two Sets as store's fields. One of them is observable other one is not.

Actual outcome:
For example if log a store.reactiveSet.intersection we will see an undefined in the console. If log a store.nonReactiveSet.intersection we will see a nonReactiveSet ƒ symmetricDifference() { [native code] } (there I used Chrome 123)
Obviously for other Set's methods result is the same:

How to reproduce the issue:

Run code from provided sandbox. Look into browser's console

Versions

Mobx 6.12.1

Also I propose made this as part of Mobx 7 roadmap #3796

[inoyakaigor]

Also I think there is only one place for changes that will add support the new methods: mobx/src/types/observableset.ts and it means it is not a big deal but can't imagine what exactly future code should look like?

[mweststrate]

Great idea. PR welcome. In many cases these kind of operations can be implemented by calling the original version on the Set prototype with iterator of the observable set.

[inoyakaigor]

Also I just realised that there also should be added Object.groupBy and Map.groupBy