introduce a moveField jsonata function

[aeberhart]

quite often, we need to "move" fields like this:

{
  x: 1,   ---- move this
  arr:[
    { ... },    --in here
    { ... }    --and in here
  ]
}

The command could be:

$moveField($, "x", "arr")

The "normal" jsonata way would be to use a variable / the parent operator in conjunction with $merge which can be a bit lengthy

[aeberhart]

if "arr" is a regular object this must work as well of course

[aeberhart]

$flatten already does something similar