Improve class initialization barrier in TemplateTable::_new for RISC-V

The class initialization barrier in TemplateTable::_new fast path check ensures that the class being instantiated is fully initialized. It can be improved by introducing additional fast path check when current thread is initializer thread as MacroAssembler::clinit_barrier() does. It avoids repeated calls into interpreter runtime for classes being initialized.

This improvement should be applied to all platforms that support fast class initialization.