[JVMCI] Add possibility to convert object JavaConstant to jobject.

For the Truffle runtime to be a standard module on the JVM module path, it must not have a dependency on the `jdk.internal.vm.ci` module. One necessary modification involves unpacking the Java constant. On the Truffle runtime side, the use of the `jdk.vm.ci.meta.JavaConstant` class must be removed, and the libjvmci compiler must pass an already unpacked Java constant to the Truffle runtime. The `jdk.vm.ci.hotspot.HotSpotObjectConstant` must be unpacked into a HotSpot heap JNI jobject that is passed as an argument to the host using the JNI invocation API.