HPCC-10674 ECL support for writing JSON files

Signed-off-by: Anthony Fishbeck <anthony.fishbeck@lexisnexis.com>
w

Signed-off-by: Anthony Fishbeck <anthony.fishbeck@lexisnexis.com>
HPCC-11922 DESDL add JSON Support

Add rewindTo IXmlWriterExt method
Add JSON builder, JSON test
Add JSON helper functions to esp/services/common

Signed-off-by: rpastrana <rodrigo.pastrana@lexisnexis.com>