Work around the fact that GraalVM detects that DataSize is safe to initialize at build time

[snicoll]

Building a simple command-line leads to:

Error: Classes that should be initialized at run time got initialized during image building:
 org.springframework.util.unit.DataSize was unintentionally initialized at build time. To see why org.springframework.util.unit.DataSize got initialized use --trace-class-initialization=org.springframework.util.unit.DataSize

com.oracle.svm.core.util.UserError$UserException: Classes that should be initialized at run time got initialized during image building:
 org.springframework.util.unit.DataSize was unintentionally initialized at build time. To see why org.springframework.util.unit.DataSize got initialized use --trace-class-initialization=org.springframework.util.unit.DataSize

	at com.oracle.svm.core.util.UserError.abort(UserError.java:73)
	at com.oracle.svm.hosted.classinitialization.ConfigurableClassInitialization.checkDelayedInitialization(ConfigurableClassInitialization.java:555)
	at com.oracle.svm.hosted.classinitialization.ClassInitializationFeature.duringAnalysis(ClassInitializationFeature.java:167)
	at com.oracle.svm.hosted.NativeImageGenerator.lambda$runPointsToAnalysis$10(NativeImageGenerator.java:704)
	at com.oracle.svm.hosted.FeatureHandler.forEachFeature(FeatureHandler.java:74)
	at com.oracle.svm.hosted.NativeImageGenerator.lambda$runPointsToAnalysis$11(NativeImageGenerator.java:704)
	at com.oracle.graal.pointsto.PointsToAnalysis.runAnalysis(PointsToAnalysis.java:755)
	at com.oracle.svm.hosted.NativeImageGenerator.runPointsToAnalysis(NativeImageGenerator.java:702)
	at com.oracle.svm.hosted.NativeImageGenerator.doRun(NativeImageGenerator.java:537)
	at com.oracle.svm.hosted.NativeImageGenerator.run(NativeImageGenerator.java:494)
	at com.oracle.svm.hosted.NativeImageGeneratorRunner.buildImage(NativeImageGeneratorRunner.java:426)
	at com.oracle.svm.hosted.NativeImageGeneratorRunner.build(NativeImageGeneratorRunner.java:587)
	at com.oracle.svm.hosted.NativeImageGeneratorRunner.main(NativeImageGeneratorRunner.java:126)
	at com.oracle.svm.hosted.NativeImageGeneratorRunner$JDK9Plus.main(NativeImageGeneratorRunner.java:617)

This looks wrong and could be addressed in Graal. In the meantime we'll add a flag to prevent that from happening.