[BUG] GpuBatchScanExec only reports output row metrics

[jlowe]

Describe the bug
GpuBatchScanExec is supposed to show the same types of GPU-related metrics as FileSourceScanExec (e.g.: buffer time, GPU decode time, output batches, etc.) but output rows are the only metrics shown even with spark.rapids.sql.metrics.level=DEBUG.

Steps/Code to reproduce bug

• Set spark.rapids.sql.metrics.level to DEBUG
• Set spark.sql.sources.useV1SourceList to ""
• Run a simple query to scan a Parquet file (e.g.: spark.read.parquet("tests/src/test/resources/timestamp-date-test.parquet").collect()
• Examine the SQL UI and note that only output rows are shown as a metric for the GPU batch scan, e.g.:

Expected behavior
All of the metrics setup in GpuBatchScanExecMetrics should appear in the SQL UI for the GpuBatchScan node rather than just output rows.

Environment details (please complete the following information)
Replicated the problem with Spark 3.1.2 and Spark 3.2.1