Make ISettableGridView.Fill faster for ArrayView

[Chris3606]

• Currently, ISettableGridView.Fill handles ArrayView like any other grid view, by simply setting the elements using the indexers. This is functional, but very inefficient if the type is actually an ArrayView; Array.Fill (or Array.Clear in the case that the value being filled is the default one) is much faster in these cases.

Ideally, the .Fill extension method could do similar special-case logic as BitArray to gain this efficiency, since the performance gains can be quite substantial (well worth the cost of the cast).

[Chris3606]

Note: A second (potentially better) possibility might be to remove the ISettableGridView.Fill extension method, and make it a default interface method instead, so that the derived types themselves can override it. However, this may be impossible to accomplish without a (very minor) breaking change to the API.