fix: ensure SvelteMap and SvelteSet work with generators in dev (#14103)

* fix: ensure SvelteMap and SvelteSet work with generators in dev

* add test

* better fix

* better fix

* better fix

* better fix

.changeset/selfish-chicken-argue.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: ensure SvelteMap and SvelteSet work with generators in dev

packages/svelte/src/reactivity/map.js

@@ -22,7 +22,7 @@ export class SvelteMap extends Map {
 		super();
 
 		// If the value is invalid then the native exception will fire here
-		if (DEV) new Map(value);
+		if (DEV) value = new Map(value);
 
 		if (value) {
 			for (var [key, v] of value) {

packages/svelte/src/reactivity/set.js

@@ -26,7 +26,7 @@ export class SvelteSet extends Set {
 		super();
 
 		// If the value is invalid then the native exception will fire here
-		if (DEV) new Set(value);
+		if (DEV) value = new Set(value);
 
 		if (value) {
 			for (var element of value) {

packages/svelte/tests/runtime-runes/samples/svelte-set-generators/_config.js

@@ -0,0 +1,9 @@
+import { test } from '../../test';
+
+export default test({
+	compileOptions: {
+		dev: true
+	},
+
+	html: `1`
+});

packages/svelte/tests/runtime-runes/samples/svelte-set-generators/main.svelte

@@ -0,0 +1,14 @@
+<script>
+	import { SvelteSet } from 'svelte/reactivity';
+
+	function *generator() {
+		yield 1;
+	}
+
+	let gen = new SvelteSet(generator());
+</script>
+
+{#each gen as item}
+	{item}
+{/each}
+