Hide Inline Assist button if assistant.button is disabled (#7932)

This PR adds check for `assistant.button` setting in quick bar, to hide
it when the setting is set to false. It seems that the setting can be a
separate one, I would be happy to add it if needed.

Release Notes:

- Improved `assistant.button` setting so that `Inline Assist` button in
editor quick bar is also hidden
([#4500](https://github.com/zed-industries/zed/issues/4500)).

crates/quick_action_bar/src/quick_action_bar.rs

@@ -1,3 +1,4 @@
+use assistant::assistant_settings::AssistantSettings;
 use assistant::{AssistantPanel, InlineAssist};
 use editor::{Editor, EditorSettings};
 
@@ -126,7 +127,9 @@ impl Render for QuickActionBar {
             .gap_2()
             .children(inlay_hints_button)
             .children(search_button)
-            .child(assistant_button)
+            .when(AssistantSettings::get_global(cx).button, |bar| {
+                bar.child(assistant_button)
+            })
     }
 }