Suggestions for include paths creates detached pop-up window on Wayland

When typing an include path, the suggestion list for completion will open in a separate detached window on Wayland for the second completion.

Steps to reproduce:

1. Type #include < to start an include statement.
2. Start typing a path, then either choose an option with tab or type it out with a closing / for the first part of the path.
3. For the next part of the path, the suggestions will open in a separate detached pop-up.

In this screenshot I moved the window close to the code to demonstrate the issue, but in practice it often pops up in a corner of the screen based on where the Window Manager deems the "best" location for a new window.

The first path suggestion shows next to the #include as expected, as do all the other suggestion pop-ups I've tried thus far. However, for the first suggestion the contents of the pop-up will often be an invalid surface that doesn't show the options.

(EDIT: This seems to be a common issue with all pop-up windows on Wayland, I created QTCREATORBUG-30850 to cover that separately)

The behavior seems correct when using X11.