Unconstrain the IME popup when it appeared, resized, requested to

repositioned

- places the IME popup correctly.
- adjusts its position to considering the output (screen) rect.
  - offset if right edge overflows
  - flip vertically if bottom edge overflows

src/wayland/handlers/compositor.rs

@@ -281,6 +281,10 @@ impl CompositorHandler for State {
 
         if let Some(popup) = self.common.popups.find_popup(surface) {
             xdg_popup_ensure_initial_configure(&popup);
+            // The IME popup need to be repositioned when the size changed
+            if let PopupKind::InputMethod(_) = popup {
+                shell.unconstrain_popup(&popup);
+            }
             return;
         }