Add `set` alias for `next` on `BehaviorSubject`

Per this discussion on Twitter

Basically, svelte has amazing support for RxJS. Particularly in reading from RxJS observables.

This very small addition to RxJS would enable Svelte users to very conveniently trigger reactive updates through RxJS.

Proposal

Just alias next as set on BehaviorSubject. (I don’t see a reason yet to add it to all subjects).

That would enable Svelte users to simply bind to them in their templates.

cc/ @Rich-Harris

Other things

It’s probably worth discussion with Svelte experts if this solves a big enough use case for them to be a valid change, and/or what other use cases we might need to consider.

[benlesh]

So after discussion with the core team. It seems more reasonable to create a separate package with a SvelteSubject that would behave in the way you want… it is exactly this:

class SvelteSubject extends BehaviorSubject {
	set(value) {
		super.next(value);
	}
	
	lift(operator) {
		const result = new SvelteSubject();
		result.operator = operator;
		result.source = this;
		return result;
	}
}

@Rich-Harris what do you think about us adding this to the svelte org? (I’d happily help maintain that for you)

[spierala]

Started a small project with the “SvelteSubject” and implemented the svelte stores as RxJS Observables: https://github.com/spierala/svelte-store-rxjs

• writable() returns a Writable instance. Writable extends RxJS BehaviorSubject.
• readable() and derived() return a RxJS Observable