RFR: 8253899: Make IsClassUnloadingEnabled signature match specification

[Vladimir Kempik]

Please review this change for hotspot and one test.
There is few JVMTI callback/event functions in jdk which signature doesn't match specification.
for example:
static jvmtiError JNICALL IsClassUnloadingEnabled(const jvmtiEnv* env, jboolean* enabled, ...)
but according to jvmti specs it should be:
static jvmtiError JNICALL IsClassUnloadingEnabled(const jvmtiEnv* env, ...)
same with ClassUnload(jvmtiEnv* jvmti_env, JNIEnv* jni_env, const char* name, ...)  in tests
for many years that didn't matter but with coming JEP-391 it becomes important to make it match the spec
https://developer.apple.com/documentation/apple_silicon/addressing_architectural_differences_in_your_macos_code
This commit makes the above mentioned functions to have signature matching jvmti specification

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Commit messages:
 - 8253899: Make IsClassUnloadingEnabled signature match specification + jcheck
 - 8253899: Make IsClassUnloadingEnabled signature match specification

Changes: https://git.openjdk.java.net/jdk/pull/466/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=466&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8253899
  Stats: 17 lines in 2 files changed: 15 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/466.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/466/head:pull/466

PR: https://git.openjdk.java.net/jdk/pull/466