Recursively sorts all JavaScript object properties into ES6 “own property keys”
traversal order so that when properties are enumerated by other operations, like
JSON.stringify(), they are enumerated deterministically.
Prior to ES6, enumeration order for object keys was unspecified. ES6 specifies
that all 32-bit integer indices ('0', '1', '2', and so on) be enumerated
in ascending numerical order, followed by string keys ('a', '01', and so on)
in ascending alphabetical order. But only for certain types of enumeration (for
example: Refelect.ownKeys(), not Object.keys()). Ultimately, enumeration
order is determined by each JavaScript engine, but extracting, sorting, and
re-inserting keys should yield a run-time consistent enumeration order for
like-objects.