TestFunctionsForJSON: added testFIELDFunctionWithNullValues method,
modeled on testSET_FIELDFunctionWithNullValues, but taking some existing
queries from testFIELDFunction; also added a few queries to
testSET_FIELDFunctionWithNullValues; and added a new SelectFieldProc
stored proc.
Merge remote-tracking branch 'origin/ENG-6879-more-json-set-field' into ENG-6979-json-index-limit
ENG-6979, ENG-6978 Enforce JSON array index limit of 500000 ONLY for SET_FIELD, adjust tests for different failure modes.