Allow the keybinding context to detect the terminal vi_mode (#26236)

Release Notes:

- Added support for detecting the vi_mode in the keybinding context. Now
we can define and use the keybinding when the terminal is in vi_mode.


https://github.com/user-attachments/assets/a927b6c9-c634-4739-9502-8457614d9a90

crates/terminal/src/terminal.rs

@@ -1911,6 +1911,10 @@ impl Terminal {
             }
         }
     }
+
+    pub fn vi_mode_enabled(&self) -> bool {
+        self.vi_mode_enabled
+    }
 }
 
 // Helper function to convert a grid row to a string