Input method window should not break showing desktop

With recent change of using show desktop with plasma's edit mode,
wayland input method becomes unusable when trying to type in the search
box of widget explorer. This is because the input method window will
currently break showing desktop under wayland.

Under X11, an input method window is traditionally implemented as an
override redirect window. Under Wayland, the window should be treated
similarily, but now we have a special type for input method window.

BUG: 489057
FIXED-IN: 6.1

src/workspace.cpp

@@ -1519,7 +1519,7 @@ void Workspace::focusToNull()
 
 bool Workspace::breaksShowingDesktop(Window *window) const
 {
-    return !(window->isUnmanaged() || window->isDock() || window->isDesktop() || window->belongsToDesktop());
+    return !(window->isUnmanaged() || window->isDock() || window->isDesktop() || window->belongsToDesktop() || window->isInputMethod());
 }
 
 void Workspace::setShowingDesktop(bool showing, bool animated)