Add an option to pass undefined as null instead of ClearScript.Undefined

[77it]

I'm writing a project that uses JavaScript to personalize the business logic.

As a fallback to ClearScript for non-windows platforms I support also Jint (until ClearScript will support other platforms, then I won't have to work with 2 engines anymore).

Doing some tests on null I stumbled upon the conversion of undefined parameters in ClearScript.Undefined.

I understand that there are valid reasons to convert undefined to an object ClearScript.Undefined but I like much more the Jint approach to convert all to null, that is also more compatible between engines.

Then I propose a new switch to be able to convert all to null instead of ClearScript.Undefined.

I've prepared a fiddle to show a working test case (with the other engine).

Thanks for what you could do about my proposal.

[ClearScriptLib]

Version 6.0.1 adds ScriptEngine.UndefinedImportValue and makes Undefined.Value public.