keyboard: Synchronize input method state after toggling completion

Make the input method synchronize its state after the engine changes
resulting from completion being toggled.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2512>

js/misc/inputMethod.js

@@ -352,4 +352,15 @@ var InputMethod = GObject.registerClass({
             return false;
         }
     }
+
+    update() {
+        if (!this._context)
+            return;
+        this._updateCapabilities();
+        this._context.set_content_type(this._purpose, this._hints);
+        this._context.set_cursor_location(
+            this._cursorRect.x, this._cursorRect.y,
+            this._cursorRect.width, this._cursorRect.height);
+        this._emitRequestSurrounding();
+    }
 });