Added setItemIndexInParent and getItemIndexInParent functions to Tree… #732

Job	Run time
android-sfml-graphics	2m 51s
ios-sdl	4m 13s
android-sdl	7m 23s
ios-sfml-graphics	48s
linux	5m 6s
linux-latest-dev	4m 21s
linux-oldest	3m 11s
linux-per-backend	5m 34s
windows	2m 56s
macos	1m 48s
windows-clang	5m 11s
windows-oldest	7m 14s
windows-static-mt	5m 17s
nightly-build-windows-visual-studio	8m 36s
	1h 4m 29s

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