[SPARK-9104][CORE] Expose Netty memory metrics in Spark

## What changes were proposed in this pull request?

This PR exposes Netty memory usage for Spark's `TransportClientFactory` and `TransportServer`, including the details of each direct arena and heap arena metrics, as well as aggregated metrics. The purpose of adding the Netty metrics is to better know the memory usage of Netty in Spark shuffle, rpc and others network communications, and guide us to better configure the memory size of executors.

This PR doesn't expose these metrics to any sink, to leverage this feature, still requires to connect to either MetricsSystem or collect them back to Driver to display.

## How was this patch tested?

Add Unit test to verify it, also manually verified in real cluster.

Author: jerryshao <sshao@hortonworks.com>

Closes #18935 from jerryshao/SPARK-9104.