improve flutter floating window handling #5

Job	Run time
build (ubuntu-24.04, ci-dev-qt6, 6.3.*)	22m 58s
build (ubuntu-24.04, ci-release-qt6, 6.3.*)	5m 57s
build (ubuntu-24.04, ci-qtwidgets-qt6, 6.3.*)	2m 38s
build (ubuntu-24.04, ci-qtquick-qt6, 6.3.*)	1m 11s
build (ubuntu-24.04, ci-dev-static-qt6, 6.3.*)	23m 25s
build (windows-latest, ci-dev-qt6, 6.3.*)	26m 0s
build (windows-latest, ci-release-qt6, 6.3.*)	5m 7s
build (windows-latest, ci-qtwidgets-qt6, 6.3.*)	3m 37s
build (windows-latest, ci-qtquick-qt6, 6.3.*)	3m 36s
build (windows-latest, ci-dev-static-qt6, 6.3.*)	26m 54s
build (macos-15, ci-dev-qt6, 6.3.*)	20m 59s
build (macos-15, ci-release-qt6, 6.3.*)	1m 52s
build (macos-15, ci-qtwidgets-qt6, 6.3.*)	1m 15s
build (macos-15, ci-qtquick-qt6, 6.3.*)	1m 16s
build (macos-15, ci-dev-static-qt6, 6.3.*)	20m 59s
build (ubuntu-latest, ci-python-qt6, 6.6.0, 0, llvm, shiboken6-generator==6.6.0 pyside6==6.6.0)	4m 24s
	2h 52m 8s

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