Handle combined instrument states of ENABLED and/or TIMED:
ENABLED TIMED
1 1 Aggregate stats, increment counter
1 0 Increment counter
0 1 Do nothing
0 0 Do nothing
storage/perfschema/pfs.cc:
Aggregate stats only if state is both ENABLED and TIMED. If ENABLED
but not TIMED, only increment the value counter.
storage/perfschema/pfs_stat.h:
Split aggregate and counter increment into separate
methods for performance.