Hold a WeakViewHandle in BufferElement

Otherwise, the element never goes away because the view never goes away because the element is holding a strong reference.

Co-Authored-By: Max Brunsfeld <maxbrunsfeld@gmail.com>

zed/src/editor/buffer_view.rs

@@ -2161,8 +2161,8 @@ impl Entity for BufferView {
 }
 
 impl View for BufferView {
-    fn render<'a>(&self, app: &AppContext) -> ElementBox {
-        BufferElement::new(self.handle.upgrade(app).unwrap()).boxed()
+    fn render<'a>(&self, _: &AppContext) -> ElementBox {
+        BufferElement::new(self.handle.clone()).boxed()
     }
 
     fn ui_name() -> &'static str {