Restore truedm commit: chore: avoid microtasks when flushing sync

# Conflicts:
#	packages/svelte/src/internal/client/runtime.js

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

@@ -47,6 +47,7 @@ const handled_errors = new WeakSet();
 let is_throwing_error = false;
 
 let is_flushing = false;
+let is_flushing_sync = false;
 
 /** @type {Effect | null} */
 let last_scheduled_effect = null;
@@ -734,8 +735,10 @@ function flush_queued_effects(effects) {
 export function schedule_effect(signal) {
 	if (!is_flushing) {
 		is_flushing = true;
+		if (!is_flushing_sync) {
 			queueMicrotask(flush_queued_root_effects);
 		}
+	}
 
 	var effect = (last_scheduled_effect = signal);
 
@@ -818,7 +821,11 @@ function process_effects(root) {
  * @returns {T}
  */
 export function flushSync(fn) {
+	var previously_flushing_sync = is_flushing_sync;
+
+	try {
 		var result;
+		is_flushing_sync = true;
 
 		if (fn) {
 			is_flushing = true;
@@ -836,6 +843,9 @@ export function flushSync(fn) {
 			is_flushing = true;
 			flush_queued_root_effects();
 		}
+	} finally {
+		is_flushing_sync = previously_flushing_sync;
+	}
 }
 
 /**