Json unicode escape && preserveOrder keys sync

[aleks-f]

• JSON Stringify Unicode Escape functionality breaking change with 1.8.0 JSON Stringify Unicode Escape functionality breaking change with 1.8.0 #2137
• JSON::Object preserveOrder keys not synced on assignment JSON::Object preserveOrder keys not synced on assignment #2142

[obiltschnig]

See my inline comment.

[obiltschnig]

Maybe we should think about introducing an options enum for the various places where we use preserveInsertionOrder and escapeUnicode, and use an int options instead of a potentially growing list of bool args. If we just change the Object constructor to:

Object(int options = 0);

and define:

enum Options
{
    JSON_OPT_PRESERVE_INSERTION_ORDER = 1,
    JSON_OPT_ESCAPE_UNICODE = 2
};

Then the new constructor taking int will be backwards compatible to the one taking bool.

[Burgch]

This looks great, thanks again!