HPCC-9999 Fix efficiency issues with CQuerySetQueriesPager

1) In CQuerySetQueriesPager::getElements(), change the unlocked
connection to /QuerySets to read lock connection. 2) Revise the
getElements() to avoid re-connect to /QuerySets. 3) Revise the
getQueryRegistry() to not double lock the /QuerySets. 4) Revise
getQueryRegistryRoot() to not lock to /QuerySets twice. 5) Only
lock the /QuerySets/QuerySet if a QuerySet ID is specified. This
fix does nothing for server-side matching because the parent
properties of a query node are not reachable (there is no 'up'
axis support). For example, the parent property Alias is used to
set query's property @activated.

Signed-off-by: wangkx <kevin.wang@lexisnexis.com>