x11: don't forward key events to IME when it's disabled

Fixes #3815.

src/changelog/unreleased.md

@@ -187,3 +187,4 @@ changelog entry.
 - On macOS, fix `WindowEvent::Moved` sometimes being triggered unnecessarily on resize.
 - On MacOS, package manifest definitions of `LSUIElement` will no longer be overridden with the
   default activation policy, unless explicitly provided during initialization.
+- On X11, key events forward to IME anyway, even when it's disabled.

src/platform_impl/linux/x11/event_processor.rs

@@ -141,9 +141,15 @@ impl EventProcessor {
         F: FnMut(&ActiveEventLoop, Event),
     {
         let event_type = xev.get_type();
-
-        if self.filter_event(xev) {
-            if event_type == xlib::KeyPress || event_type == xlib::KeyRelease {
+        let key_event = event_type == xlib::KeyPress || event_type == xlib::KeyRelease;
+        let has_ime = self.target.ime.is_some();
+
+        // If we have IME disabled, don't try to `filter_event`, since only IME can consume them
+        // and forward back. This is not desired for e.g. games since some IMEs may delay the input
+        // and game can toggle IME back when e.g. typing into some text-box where latency won't
+        // really matter.
+        if (key_event && has_ime || !key_event) && self.filter_event(xev) {
+            if key_event {
                 let xev: &XKeyEvent = xev.as_ref();
                 if self.xmodmap.is_modifier(xev.keycode as u8) {
                     // Don't grow the buffer past the `MAX_MOD_REPLAY_LEN`. This could happen