Added addMultipleItems to ListBox and ComboBox + added getItemByIndex… #745

Job	Run time
android-sfml-graphics	2m 37s
ios-sdl	2m 36s
ios-sfml-graphics	58s
android-sdl	6m 18s
linux	5m 19s
linux-latest-dev	4m 47s
linux-oldest	3m 42s
linux-per-backend	5m 53s
macos	1m 49s
windows	2m 46s
windows-clang	5m 46s
windows-oldest	6m 45s
windows-static-mt	5m 16s
nightly-build-windows-visual-studio	6m 57s
	1h 1m 29s

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