linux: Fix IME panel position while enumerating input methods (#12495)

Release Notes:

- N/A

This updates the IME position every time the selection changes, this is
probably only useful when you enumerate languages with your IME.

TODO:
- ~There is a rare chance that the ime panel is not updated because the
window input handler is None.~
- ~Update IME panel in vim mode.~
- ~Update IME panel when leaving Buffer search input.~

---------

Co-authored-by: Mikayla Maki <mikayla@zed.dev>

crates/zed/src/main.rs

@@ -318,15 +318,6 @@ fn init_ui(
 }
 
 fn main() {
-    #[cfg(target_os = "windows")]
-    {
-        use zed::single_instance::*;
-        if !check_single_instance() {
-            println!("zed is already running");
-            return;
-        }
-    }
-
     let start_time = std::time::Instant::now();
     menu::init();
     zed_actions::init();
@@ -369,9 +360,19 @@ fn main() {
             }
         }
     }
-    #[cfg(not(any(target_os = "linux", target_os = "windows")))]
+
+    #[cfg(target_os = "windows")]
     {
-        use zed::only_instance::*;
+        use zed::windows_only_instance::*;
+        if !check_single_instance() {
+            println!("zed is already running");
+            return;
+        }
+    }
+
+    #[cfg(target_os = "macos")]
+    {
+        use zed::mac_only_instance::*;
         if ensure_only_instance() != IsOnlyInstance::Yes {
             println!("zed is already running");
             return;