`ModelStateDictionary` contains garbage entries for `DateTimeOffset[]`

[dougbu]

This is a regression from Beta3. I have not tested with other collecition types.

1. create a model that is a DateTimeOffset[] or that contains a property of that array type
2. create an action of the form public IActionResult Dates([FromForm(Name = "")] DateTimeOffset[] model) or whatever works for your more complex type
3. create a matching action that invokes a view submitting to above action
4. run in the debugger
5. hit Submit in the browser
6. break on the first line of the action from step 2
7. observe
8. note that even though the parameter is fully-populated and the model is valid, ModelState.IsValid is false.
9. a similar scenario using Beta3 (and [Bind(Prefix ="")] instead of [FromForm(Name = "")]) does not have Length or similar entries in the ModelState. ModelState.IsValid is true when using that version.

/cc @harshgMSFT

[danroth27]

@dougbu Is this just for DateTimeOffset[] or are other types affected as well?

[harshgMSFT]

Should be affecting anything and everything related to a collection.