Layout specification and discovery should follow the same behavior as partials

Fixes #1047
Unfortunately not. The value of `Name` is used to construct the exception message. Saying, 
> The view `/Views/MyController/Index.cshtml" could not be found
make it much easier to diagnose than saying
> The view `Index.cshtml" could not be found 
since it's not obvious if there's an user error in passing in the location or if something mutated it to remove the prefix. Additionally, `ViewLocationExpanders` could change what the view name could be, so mutating `SearchedLocations` is also incorrect.