fix: preserve getters/setters in HMR mode (#11231)

fixes #11228

.changeset/tender-rocks-walk.md

@@ -0,0 +1,5 @@
+---
+"svelte": patch
+---
+
+fix: preserve getters/setters in HMR mode

packages/svelte/src/internal/client/dev/hmr.js

@@ -28,7 +28,11 @@ export function hmr(source) {
 
 			effect = branch(() => {
 				set_should_intro(false);
-				Object.assign(instance, component(anchor, props));
+				// preserve getters/setters
+				Object.defineProperties(
+					instance,
+					Object.getOwnPropertyDescriptors(component(anchor, props))
+				);
 				set_should_intro(true);
 			});
 		});