fix: ensure tick resolves within a macrotask (#16825)

Race them against each other - in almost all cases requestAnimationFrame will fire first, but e.g. in case the window is not focused or a view transition happens, requestAnimationFrame will be delayed and setTimeout helps us resolve fast enough in that case

Fixes #16429
Fixes sveltejs/kit#14220

Author: dummdidumm

.changeset/wise-bottles-explode.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: ensure tick resolves within a macrotask

packages/svelte/src/internal/client/runtime.js

@@ -500,7 +500,13 @@ export function update_effect(effect) {
  */
 export async function tick() {
 	if (async_mode_flag) {
-		return new Promise((f) => requestAnimationFrame(() => f()));
+		return new Promise((f) => {
+			// Race them against each other - in almost all cases requestAnimationFrame will fire first,
+			// but e.g. in case the window is not focused or a view transition happens, requestAnimationFrame
+			// will be delayed and setTimeout helps us resolve fast enough in that case
+			requestAnimationFrame(() => f());
+			setTimeout(() => f());
+		});
 	}
 
 	await Promise.resolve();