Reduce number of VM_getReferenceSlotsInClass messages for JITServer

[mpirvu]

These messages are sent by the server to inquire about the offsets of the reference slots in a j9class.
This commit implements caching at the JITServer of the information received from the client. This change reduces the number of VM_getReferenceSlotsInClass by a factor of 10.

[mpirvu]

jenkins test sanity plinuxjit,xlinuxjit,zlinuxjit,alinux64jit jdk21

[mpirvu]

openjdk tests failed the VectorAPI tests on all platforms. This is a known issue.
plinux has failed

22:19:27  +++ j9vm.test.classloading.K64MethodTest: +++
22:19:27  command: /home/jenkins/workspace/Test_openjdk21_j9_sanity.functional_ppc64le_linux_jit_Personal_testList_0/jdkbinary/j2sdk-image/bin/java -XX:+UseJITServer -Xjit -Xgcpolicy:gencon -Xnocompressedrefs  -Xdump -Xms64m -Xmx64m -classpath /home/jenkins/workspace/Test_openjdk21_j9_sanity.functional_ppc64le_linux_jit_Personal_testList_0/aqa-tests/TKG/../../jvmtest/functional/VM_Test/VM_Test.jar:/home/jenkins/workspace/Test_openjdk21_j9_sanity.functional_ppc64le_linux_jit_Personal_testList_0/../../testDependency/lib/asm-all.jar j9vm.test.classloading.K64MethodTest 
22:19:27  
22:20:05  Cancelling nested steps due to timeout
22:20:05  Sending interrupt signal to process
22:20:14  -----------------------------------
22:20:14  J9vmTest_0_FAILED

but it looks to me that the entire sequence of tests took too much time, rather than being a true timeout

[mpirvu]

1x grinder for the plinux failure: https://openj9-jenkins.osuosl.org/job/Grinder/4102/

[mpirvu]

That grinder passed, so the so called timeout was not real. Just the tests running too slow.