linux: Show warning if file picker portal is missing (#14401)

This PR adds a warning when the file chooser couldn't be opened on Linux

It's quite confusing when trying to open a file and apparently nothing
happens:

fixes https://github.com/zed-industries/zed/issues/11089,
https://github.com/zed-industries/zed/issues/14328,
https://github.com/zed-industries/zed/issues/13753#issuecomment-2225812703,
https://github.com/zed-industries/zed/issues/13766,
https://github.com/zed-industries/zed/issues/14384,
https://github.com/zed-industries/zed/issues/14353,
https://github.com/zed-industries/zed/issues/9209


![image](https://github.com/user-attachments/assets/5acabdaa-7a9d-4225-9480-e371d20387c3)


Release Notes:

- N/A

crates/extensions_ui/src/extensions_ui.rs

@@ -12,7 +12,7 @@ use editor::{Editor, EditorElement, EditorStyle};
 use extension::{ExtensionManifest, ExtensionOperation, ExtensionStore};
 use fuzzy::{match_strings, StringMatchCandidate};
 use gpui::{
-    actions, uniform_list, AnyElement, AppContext, EventEmitter, FocusableView, FontStyle,
+    actions, uniform_list, AnyElement, AppContext, EventEmitter, Flatten, FocusableView, FontStyle,
     InteractiveElement, KeyContext, ParentElement, Render, Styled, Task, TextStyle,
     UniformListScrollHandle, View, ViewContext, VisualContext, WeakView, WhiteSpace, WindowContext,
 };
@@ -24,7 +24,6 @@ use std::time::Duration;
 use std::{ops::Range, sync::Arc};
 use theme::ThemeSettings;
 use ui::{prelude::*, ContextMenu, PopoverMenu, ToggleButton, Tooltip};
-use util::ResultExt as _;
 use workspace::item::TabContentParams;
 use workspace::{
     item::{Item, ItemEvent},
@@ -58,9 +57,23 @@ pub fn init(cx: &mut AppContext) {
                     multiple: false,
                 });
 
+                let workspace_handle = cx.view().downgrade();
                 cx.deref_mut()
                     .spawn(|mut cx| async move {
-                        let extension_path = prompt.await.log_err()??.pop()?;
+                        let extension_path =
+                            match Flatten::flatten(prompt.await.map_err(|e| e.into())) {
+                                Ok(Some(mut paths)) => paths.pop()?,
+                                Ok(None) => return None,
+                                Err(err) => {
+                                    workspace_handle
+                                        .update(&mut cx, |workspace, cx| {
+                                            workspace.show_portal_error(err.to_string(), cx);
+                                        })
+                                        .ok();
+                                    return None;
+                                }
+                            };
+
                         store
                             .update(&mut cx, |store, cx| {
                                 store