Fixed the Event Listener Leak in styles panel

Every time the Styles panel rebuilt a CSS section, `StylePropertyTreeElement` would attach a new `LOCAL_VALUE_UPDATED` listener to the `SDK.CSSProperty`. Because these listeners were never removed, they accumulated. A single style update would eventually trigger thousands of `updateTitle()` calls, causing a CPU spike.

Explicitly saving the bound listener to a private property (`#onPropertyLocalValueUpdated`) in `StylePropertyTreeElement` and
leverage the `TreeElement` framework's native `onunbind()` lifecycle method to properly remove this listener when the element is detached. 

Bug: 487901682
Change-Id: I7bb7c3e338109497df072333294d10386324892d
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/7658087
Auto-Submit: Danil Somsikov <dsv@chromium.org>
Reviewed-by: Philip Pfaffe <pfaffe@chromium.org>
Commit-Queue: Danil Somsikov <dsv@chromium.org>

Author: danilsomsikov

front_end/panels/elements/StylePropertyTreeElement.ts

@@ -2066,9 +2066,12 @@ export class StylePropertyTreeElement extends UI.TreeOutline.TreeElement {
       this.listItemElement.textContent = '';
     }
 
-    this.property.addEventListener(SDK.CSSProperty.Events.LOCAL_VALUE_UPDATED, () => {
-      this.updateTitle();
-    });
+    this.property.addEventListener(SDK.CSSProperty.Events.LOCAL_VALUE_UPDATED, this.updateTitle, this);
+  }
+
+  override onunbind(): void {
+    this.property.removeEventListener(SDK.CSSProperty.Events.LOCAL_VALUE_UPDATED, this.updateTitle, this);
+    super.onunbind();
   }
 
   async gridNames(): Promise<Set<string>> {