factor out logic duplicated between ciEnv and jvmciEnv

There is quite a lot of non-trivial logic duplicated between ciEnv and jvmciEnv that should be factored out into a single location. This will help mitigate bugs such as JDK-8191052.

Some methods such as JVMCIEnv::check_for_system_dictionary_modification and ciEnv::validate_compile_task_dependencies could be factored out into a helper in Dependencies. By the same token, the similar pieces of get_klass_by_index_impl and get_method_by_index_impl should probably be factored up into ConstantPool.