Adding start of media query validation to give more informative error messages

I'm just learning media query syntax and when you have an error in the syntax VS isn't particularly helpful as to what the problem is.

I had this:

    @media (max-width: 640px) or (max-device-width: 640px)

And it will tell you that `or` isn't valid but it was off to the internet to work out what the correct syntax is. This TagProvider will inject a message to help you out instead.