Add is date object function

[pczarn2]

Add new CF2016 Update 3 function. Reference: https://helpx.adobe.com/coldfusion/cfml-reference/coldfusion-functions/functions-in-k/isdateobject.html

[KamasamaK]

There's no need for you to keep closing your PRs. Just add a new commit for your changes. This is the 7th PR you've made to add this function.

[pczarn2]

@KamasamaK This should now be ready to merge into the main branch. Let me know if you want more changes.

[pfreitag]

Thanks @pczarn2 and also @KamasamaK for review!

[KamasamaK]

Sorry I didn't respond yet. I was waiting to hear back from Adobe but after a week still nothing -- unsurprising. It turns out that their History section is wrong about the parameter being renamed. It is supposed to be value.