Drop support for Java 11 and modernize (#934) #16

Job	Run time
Build scip-java CLI	4m 6s
maven-java17-spring-boot	2m 25s
gradle-kotlin-flowext	2m 39s
maven-kotlin-json-kotlin-maven	2m 57s
gradle-kotlin-okio	3m 16s
gradle-java21-readiness	2m 59s
bazel-java-examples	1m 37s
gradle-mixed-okio-jmh	4m 48s
	24m 47s

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