Show deleted_rows_scanned stats in verbose mode

[takabow]

The deleted_rows_scanned in QueryStats is usuful for diagnosing bottlenecks in scanned tables with many insertion and deletion.

I added deleted rows scanned section in verbose mode.

Before

spanner> select count(*) from new_orders;
+--------+
|        |
+--------+
| 835790 |
+--------+
1 rows in set (70.49 msecs)
timestamp: 2021-03-09T14:04:10.376489+09:00
cpu:       325.3 msecs
scanned:   835790 rows
optimizer: 2

After

spanner> select count(*) from new_orders;
+--------+
|        |
+--------+
| 835790 |
+--------+
1 rows in set (70.49 msecs)
timestamp:            2021-03-09T14:04:10.376489+09:00
cpu time:             325.3 msecs
rows scanned:         835790 rows
deleted rows scanned: 232750 rows
optimizer version:    2

[yfuruyama]

nit: Could you update this number to 20?

$ echo -n 'deleted rows scanned' | wc -c
      20

[yfuruyama]

LGTM, thanks!