[SPARK-4874] [CORE] Collect record count metrics

Collects record counts for both Input/Output and Shuffle Metrics. For the input/output metrics, it just appends the counter every time the iterators get accessed.

For shuffle on the write side, we count the metrics post aggregation (after a map side combine) and on the read side we count the metrics pre aggregation. This allows both the bytes read/written metrics and the records read/written to line up.

For backwards compatibility, if we deserialize an older event that doesn't have record metrics, we set the metric to -1.

Author: Kostas Sakellis <kostas@cloudera.com>

Closes #4067 from ksakellis/kostas-spark-4874 and squashes the following commits:

bd919be [Kostas Sakellis] Changed 'Records Read' in shuffleReadMetrics json output to 'Total Records Read'
dad4d57 [Kostas Sakellis] Add a comment and check to BlockObjectWriter so that it cannot be reopend.
6f236a1 [Kostas Sakellis] Renamed _recordsWritten in ShuffleWriteMetrics to be more consistent
70620a0 [Kostas Sakellis] CR Feedback
17faa3a [Kostas Sakellis] Removed AtomicLong in favour of using Long
b6f9923 [Kostas Sakellis] Merge AfterNextInterceptingIterator with InterruptableIterator to save a function call
46c8186 [Kostas Sakellis] Combined Bytes and # records into one column
57551c1 [Kostas Sakellis] Conforms to SPARK-3288
6cdb44e [Kostas Sakellis] Removed the generic InterceptingIterator and repalced it with specific implementation
1aa273c [Kostas Sakellis] CR Feedback
1bb78b1 [Kostas Sakellis] [SPARK-4874] [CORE] Collect record count metrics

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