Test if a Window or control is visible and not covered by other windows or controls.
Maybe useful to someone:
; Inspired by https://stackoverflow.com/questions/5445889/get-which-process-window-is-actually-visible-in-c-sharp
; GW_HWNDPREV always returned window "Default IDM" on my system, so I had to take a different approach
#include <GUIConstantsEx.au3>
#include <WinAPISysWin.au3>
#include <WinAPIGdi.au3>
#include <WindowsC