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/context.rs

@@ -3548,7 +3548,7 @@ mod tests {
             _query: String,
             _cancel: Arc<AtomicBool>,
             _workspace: Option<WeakView<Workspace>>,
-            _cx: &mut AppContext,
+            _cx: &mut WindowContext,
         ) -> Task<Result<Vec<ArgumentCompletion>>> {
             Task::ready(Ok(vec![]))
         }