[SPARK-9824] [CORE] Fix the issue that InternalAccumulator leaks WeakReference

`InternalAccumulator.create` doesn't call `registerAccumulatorForCleanup` to register itself with ContextCleaner, so `WeakReference`s for these accumulators in `Accumulators.originals` won't be removed.

This PR added `registerAccumulatorForCleanup` for internal accumulators to avoid the memory leak.

Author: zsxwing <zsxwing@gmail.com>

Closes #8108 from zsxwing/internal-accumulators-leak.