Add Caps Lock support (#30470)

Closes #21700

Release Notes:

- Added caps lock support and show a warning if the user is entering an
SSH password with Caps Lock enabled

---------

Co-authored-by: Mikayla Maki <mikayla@zed.dev>
Co-authored-by: Mikayla Maki <mikayla.c.maki@gmail.com>
Co-authored-by: 张小白 <364772080@qq.com>

crates/gpui/src/platform/test/window.rs

@@ -153,6 +153,10 @@ impl PlatformWindow for TestWindow {
         crate::Modifiers::default()
     }
 
+    fn capslock(&self) -> crate::Capslock {
+        crate::Capslock::default()
+    }
+
     fn set_input_handler(&mut self, input_handler: PlatformInputHandler) {
         self.0.lock().input_handler = Some(input_handler);
     }