ui: Expose keybinding visibility (#63770)

`KeyBinding::set_default_visibility` lets applications suppress
keybinding labels, but the current visibility value is private to
`KeyBinding::render`. Applications that compose related modifier hints
from lower-level UI elements cannot follow the same presentation policy.

Expose the existing visibility query without changing its behavior. This
lets those callers omit their complete hint, including accompanying text
and spacing, while sharing the same application-wide source of truth.

Release Notes:

- N/A

crates/ui/src/components/keybinding.rs

@@ -116,7 +116,8 @@ impl KeyBinding {
         cx.refresh_windows();
     }
 
-    fn default_visibility(cx: &mut App) -> bool {
+    /// Returns whether keybindings are visible application-wide.
+    pub fn default_visibility(cx: &mut App) -> bool {
         cx.default_global::<KeyBindingVisibility>().0
     }