interpreter: Fix wrong parent item tree of the PopupWindow (#6448)

When calling `popup.show()` the parent itemtree of the popup should be
the one from the parent in which the PopupWindow is declared in the
source, and not the one of the context in which the `popup.show()` code
appears.

Part of issue #6426.
This happens to fix the issue as presented there.

But there is another issue in which we still crash when trying to access
global from a popup who's parent has been deleted because the interpreter 
needs access to the root item tree to access the globals

internal/interpreter/eval.rs

@@ -619,7 +619,7 @@ fn call_builtin_function(
                         )
                     },
                     popup.close_on_click,
-                    component.self_weak().get().unwrap().clone(),
+                    enclosing_component.self_weak().get().unwrap().clone(),
                     component.window_adapter(),
                     &parent_item,
                 );