Fix popup reposition damage
When repositioning popups (which GTK4 does) we so far damaged the whole surface tree which was a) too much damage b) didn't work when the popup was was outside the parent. Based on work in !623 (merged) we can fix this. Can be tested with e.g. chatty when floating and openning the spell check window.
Draft as it needs !623 (merged), should be fine otherwise.