Fix multiple SGEN_LOG to correctly scale elapsed time in usec. (#16485)
Several SGEN_LOG entries logged usec based on result returend from TV_ELAPSED.
On SGEN's implementation of TV_ELAPSED, the result is not scaled to usec
but returned as 100ns ticks. This was not handled correctly by SGEN_LOG,
but other measures, like profile counters and SGEN binary protocol handles
it correctly.
Fix will adjust the SGEN_LOG calls currently presenting usec to correctly
scale the result. Fix also adds one additional logging measuring total
amount of time spend scanning thread data.