[cleanup] Use Comparator.comparing

Done with the JDT UI cleanup action.

Change-Id: I314795a98be3d54e54c5039a3b0d11496450742d
Signed-off-by: Lars Vogel <Lars.Vogel@vogella.com>
Reviewed-on: https://git.eclipse.org/r/c/platform/eclipse.platform.resources/+/183554
Tested-by: Platform Bot <platform-bot@eclipse.org>
Reviewed-by: Hannes Wellmann <wellmann.hannes1@gmx.net>