More tests for alex innovation json

Added tests of the JSON function SET_FIELD, plus a few more for FIELD, including with dotted path and/or array index notation, and with dot and bracket characters not used in that way (and therefore escaped with a backslash), and using numeric, floating point data.
I'd distinguish an empty string doc or path here from a SQL null doc or path, and restore the conventional null-in -> null-out semantics when either argument is null.