add test for breaking from a reactive block

test/runtime/samples/reactive-block-break/_config.js

@@ -0,0 +1,3 @@
+export default {
+	html: `<h1>1 2</h1>`
+};

test/runtime/samples/reactive-block-break/main.svelte

@@ -0,0 +1,14 @@
+<script>
+	let foo = 0;
+	let bar;
+	$: {
+		bar = foo + 1;
+		if (foo) {
+			break $;
+		}
+		bar = foo + 2;
+	}
+	foo = 1;
+</script>
+
+<h1>{foo} {bar}</h1>