Improve /tabs completion workflow (#16168)

Follow-up of https://github.com/zed-industries/zed/pull/16154

Reworks /tabs arguments to allow:
* current tab by default, if no arguments are present
* fuzzy-matching over paths of the related tabs
* `all` case to insert all tabs at once

Release Notes:

- N/A

crates/assistant/src/slash_command/fetch_command.rs

@@ -8,7 +8,7 @@ use assistant_slash_command::{
     ArgumentCompletion, SlashCommand, SlashCommandOutput, SlashCommandOutputSection,
 };
 use futures::AsyncReadExt;
-use gpui::{AppContext, Task, WeakView};
+use gpui::{Task, WeakView};
 use html_to_markdown::{convert_html_to_markdown, markdown, TagHandler};
 use http_client::{AsyncBody, HttpClient, HttpClientWithUrl};
 use language::LspAdapterDelegate;
@@ -120,7 +120,7 @@ impl SlashCommand for FetchSlashCommand {
         _query: String,
         _cancel: Arc<AtomicBool>,
         _workspace: Option<WeakView<Workspace>>,
-        _cx: &mut AppContext,
+        _cx: &mut WindowContext,
     ) -> Task<Result<Vec<ArgumentCompletion>>> {
         Task::ready(Ok(Vec::new()))
     }