keyboardManager.js: Don't wait on ibus' set_global_engine_async()

to return when switching between xkb layouts.

This can incur at noticeable delay when switching, so skip it
unless it's necessary.

ref: #13384, #13428 (though I think in both of these the comments
are not always referring to the same issues, since there are
multiple keybinding types at work here).

Author: mtwebster

js/ui/keyboardManager.js

@@ -636,14 +636,18 @@ var InputSourceManager = class {
         if (is === this._currentSource)
             return;
 
+        // A switch between two xkb layouts doesn't change the ibus engine.
+        let xkbToXkb = this._currentSource?.type == INPUT_SOURCE_TYPE_XKB &&
+                       is.type == INPUT_SOURCE_TYPE_XKB;
+
         // The focus changes during holdKeyboard/releaseKeyboard may trick
         // the client into hiding UI containing the currently focused entry.
         // So holdKeyboard/releaseKeyboard are not called when
         // 'set-content-type' signal is received.
         // E.g. Focusing on a password entry in a popup in Xorg Firefox
         // will emit 'set-content-type' signal.
         // https://gitlab.gnome.org/GNOME/gnome-shell/issues/391
-        if (!this._reloading)
+        if (!this._reloading && !xkbToXkb)
             holdKeyboard();
         this._keyboardManager.apply(is.xkbId);
 
@@ -659,10 +663,18 @@ var InputSourceManager = class {
         else
             engine = 'xkb:us::eng';
 
-        if (!this._reloading)
-            this._ibusManager.setEngine(engine, releaseKeyboard);
-        else
+        if (this._reloading) {
+            this._ibusManager.setEngine(engine);
+        } else if (xkbToXkb) {
+            // muffin freezes the keyboard for grp: switches (via
+            // modifiers-accelerator-activated) and delegates the unfreeze to
+            // this handler, so release it even though we skipped holdKeyboard -
+            // synchronously, without waiting on the ibus round-trip.
             this._ibusManager.setEngine(engine);
+            releaseKeyboard();
+        } else {
+            this._ibusManager.setEngine(engine, releaseKeyboard);
+        }
 
         if (is.type == INPUT_SOURCE_TYPE_IBUS && (is.id === this._currentSource?.id)) {
             this._ibusManager.refreshCurrentEngineProperties();