Run slash commands both on enter and on argument completion that requires it (#16283)

Release Notes:

- N/A

crates/assistant/src/assistant_panel.rs

@@ -2081,7 +2081,7 @@ impl ContextEditor {
                     }
 
                     editor.insert(&format!("/{name}"), cx);
-                    if command.requires_argument() {
+                    if command.accepts_arguments() {
                         editor.insert(" ", cx);
                         editor.show_completions(&ShowCompletions::default(), cx);
                     }
@@ -2094,6 +2094,10 @@ impl ContextEditor {
     }
 
     pub fn confirm_command(&mut self, _: &ConfirmCommand, cx: &mut ViewContext<Self>) {
+        if self.editor.read(cx).has_active_completions_menu() {
+            return;
+        }
+
         let selections = self.editor.read(cx).selections.disjoint_anchors();
         let mut commands_by_range = HashMap::default();
         let workspace = self.workspace.clone();