Add documentation for preprocessors #11867

Job	Run time
lint	5m 14s
flaky-tests	12m 22s
build-ubicloud-standard-8-jdk-21-snapshot-blockhound	24m 8s
build-macos-latest-jdk-21	54m 4s
site	6m 5s
build-windows-latest-jdk-21	59m 24s
build-ubicloud-standard-8-jdk-8	14m 45s
build-ubicloud-standard-8-jdk-11	18m 7s
build-ubicloud-standard-8-jdk-17-leak	17m 26s
build-ubicloud-standard-8-jdk-17-min-java-11	20m 10s
build-ubicloud-standard-8-jdk-17-min-java-17-coverage	20m 50s
	4h 12m 35s

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