ClassListParser::current should be used only by main thread

During -Xshare:dump, ClassListParser::current() should be used only by the main thread, which has created the only ClassListParser instance. Accessing it from other threads could cause intermittent failures. We observed this only on certain hosts with -Xcomp.

The following 15 tests failed in the JDK17 CI with SIGSEGV:

runtime/cds/appcds/SharedBaseAddress.java
runtime/cds/appcds/PackageSealing.java
runtime/cds/appcds/NonExistClasspath.java
runtime/cds/appcds/MultiReleaseJars.java
runtime/cds/appcds/MismatchedPathTriggerMemoryRelease.java
runtime/cds/appcds/DumpClassListWithLF.java
runtime/cds/appcds/BootClassPathMismatch.java
runtime/cds/appcds/ArchiveRelocationTest.java
runtime/cds/appcds/sharedStrings/InvalidFileFormat.java
runtime/cds/appcds/sharedStrings/ExerciseGC.java
runtime/cds/appcds/jvmti/transformRelatedClasses/TransformInterfaceImplementorAppCDS.java
runtime/cds/appcds/javaldr/GCSharedStringsDuringDump.java
runtime/cds/appcds/dynamicArchive/DynamicArchiveRelocationTest.java
runtime/cds/appcds/customLoader/ClassListFormatD.java
runtime/cds/appcds/customLoader/ClassListFormatB.java

The following 3 tests failed with other errors:

runtime/cds/serviceability/ReplaceCriticalClassesForSubgraphs.java
runtime/cds/appcds/VerifierTest_1B.java
runtime/cds/appcds/dynamicArchive/LambdaForClassInBaseArchive.java

The test task's JVM args are:

-Xcomp -XX:+CreateCoredumpOnCrash -ea -esa -XX:CompileThreshold=100 -XX:+UnlockExperimentalVMOptions -server -XX:+TieredCompilation -XX:-UseBiasedLocking

Starting this bug as a P2 due to the sheer number of failures.