HPCC-11033 Load WU timer info in one call for WU Details

The existing ECL WU Details page takes a long time to load when a
WU has many timer items or helper files. The load time is improved
by this fix. 1. In this fix, the WUinfo code will use WU Statistics
data about timers if the Statistics data is available. 2. If a WU does
not have the Statistics data, an new interface IConstWUTimerIterator
is added to get the timer data in one call. For an ECL WU with 4635
timer items, the time to read timer data is decreased from >100
seconds to <0.1 second. 3. This fix also reduces the time of reading
helper data by combining 2 file lookup calls into one call.

Signed-off-by: Kevin Wang kevin.wang@lexisnexis.com