Fix LazyRandom for native code generation tools

[Maia-Everett]

Trying to generate a native code image with GraalVM in code that uses TimeBasedEpochGenerator results in this exception:

Caused by: org.graalvm.compiler.java.BytecodeParser$BytecodeParserError: com.oracle.graal.pointsto.constraints.UnsupportedFeatureException: Detected an instance of Random/SplittableRandom class in the image heap. Instances created during image generation have cached seed values and don't behave as expected.  To see how this object got instantiated use --trace-object-instantiation=java.security.SecureRandom. The object was probably created by a class initializer and is reachable from a static field. You can request class initialization at image runtime by using the option --initialize-at-run-time=<class-name>. Or you can write your own initialization methods and call them explicitly from your main entry point.
        at parsing com.fasterxml.uuid.impl.LazyRandom.sharedSecureRandom(LazyRandom.java:12)
        at jdk.internal.vm.compiler/org.graalvm.compiler.java.BytecodeParser.throwParserError(BytecodeParser.java:2518)
        at org.graalvm.nativeimage.builder/com.oracle.svm.hosted.phases.SharedGraphBuilderPhase$SharedBytecodeParser.throwParserError(SharedGraphBuilderPhase.java:110)
        at jdk.internal.vm.compiler/org.graalvm.compiler.java.BytecodeParser.iterateBytecodesForBlock(BytecodeParser.java:3393)
        at jdk.internal.vm.compiler/org.graalvm.compiler.java.BytecodeParser.handleBytecodeBlock(BytecodeParser.java:3345)
        at jdk.internal.vm.compiler/org.graalvm.compiler.java.BytecodeParser.processBlock(BytecodeParser.java:3190)
        at jdk.internal.vm.compiler/org.graalvm.compiler.java.BytecodeParser.build(BytecodeParser.java:1138)
        at jdk.internal.vm.compiler/org.graalvm.compiler.java.BytecodeParser.buildRootMethod(BytecodeParser.java:1030)
        at jdk.internal.vm.compiler/org.graalvm.compiler.java.GraphBuilderPhase$Instance.run(GraphBuilderPhase.java:97)
        at org.graalvm.nativeimage.builder/com.oracle.svm.hosted.phases.SharedGraphBuilderPhase.run(SharedGraphBuilderPhase.java:84)

This happens because the TimeBasedEpochGenerator constructor initializes the LazyRandom class unconditionally, even if it is never actually used because the constructor is never passed a null Random instance, and LazyRandom eagerly creates a SecureRandom instance in a static final field.

Changing the TimeBasedEpochGenerator constructor would break backward compatibility, so instead I have opted to modify LazyRandom so that SecureRandom initialization actually occurs lazily. With this, the code path that results in initializing LazyRandom.shared is never hit at code generation phase, and so native image generation works as expected.

[cowtowncoder]

Thank you @Maia-Everett for contributing this! I hope to review it soon, sounds like a useful improvement.

[cowtowncoder]

Since this is not called very often, I think I'll modify this to use straight synchronization instead of double-locking.