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.
There should be a short test function exercising the error catching for some easily mistyped invalid cases:

- "array[]"
- "array["
- "array[123"
- "array[xyz]"
- "array[-2]"
- "array[2]" on a 2 element array (should return null)
- "array[1000000000000000000000]" (overflow index as opposed to slightly out of range index)
- "nonarray[0]"