Draw crosshair and pointSize consistently regardless the zoom level #927

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Run time

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Job	Run time
build (macos-latest, 3.9, pyqt5)	3m 9s
build (macos-latest, 3.9, pyside2)	2m 42s
build (ubuntu-latest, 3.9, pyqt5)	3m 51s
build (ubuntu-latest, 3.9, pyside2)	2m 27s
build (windows-latest, 3.9, pyqt5)	6m 9s
build (windows-latest, 3.9, pyside2)	4m 49s
	23m 7s