This reverts commit 40330b8f0a.
It was a bad idea to use QFlatMap here, because it is a sorted map, but
we need to keep the passive grabbers in the same order as the grabs happened.
So need to go back to an earlier version of the patch that uses two parallel QLists.
Pick-to: 6.1
Change-Id: I9e6013c2565986fe1eb9fd754f8259766f83bee5
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>