fix: autoResize issue with v-show by implementing ResizeObserver

- Problem: When using v-show to toggle the visibility of the Textarea component, the auto-resize functionality fails because this.$el.offsetParent returns null when the element is hidden.
- Solution: Added a ResizeObserver to detect size changes and adjusted the resize logic to handle visibility changes. Now, the Textarea component correctly auto-resizes when it becomes visible and when its content or parent size changes.

packages/primevue/src/textarea/Textarea.vue

@@ -15,17 +15,27 @@ export default {
         $pcFluid: { default: null }
     },
     mounted() {
-        if (this.$el.offsetParent && this.autoResize) {
-            this.resize();
+        if (this.autoResize) {
+            this.observer = new ResizeObserver(() => {
+                this.resize();
+            });
+            this.observer.observe(this.$el);
         }
     },
     updated() {
-        if (this.$el.offsetParent && this.autoResize) {
+        if (this.autoResize) {
             this.resize();
         }
     },
+    onBeforeUnmount() {
+        if (this.observer) {
+            this.observer.disconnect();
+        }
+    },
     methods: {
         resize() {
+            if (!this.$el.offsetParent) return;
+
             this.$el.style.height = 'auto';
             this.$el.style.height = this.$el.scrollHeight + 'px';