Allow a `const ArrayHandle` to be reallocated
Previously, the `Allocate` method of `ArrayHandle` was _not_ declared as `const`. Likewise, the methods that depended on `Allocate`, namely `ReleaseResources` and `PrepareForOutput` were also not declared `const`. The main consequence of this was that if an `ArrayHandle` were passed as a constant reference argument to a method (e.g. `const ArrayHandle<T>& arg`), then the array could not be reallocated. This seems right at first blush. However, we have changed these methods to be `const` so that you can in fact reallocate the `ArrayHandle`. This is because the `ArrayHandle` is in principle a pointer to an array pointer. Such a structure in C will allow you to change the pointer to the array, and so in this context it makes sense for `ArrayHandle` to support that as well. Although this distinction will certainly be confusing to users, we think this change is correct for a variety of reasons. 1. This change makes the behavior of `ArrayHandle` consistent with the behavior of `UnknownArrayHandle`. The latter needed this behavior to allow `ArrayHandle`s to be passed as output arguments to methods that get automatically converted to `UnknownArrayHandle`. 2. Before this change, a `const ArrayHandle&` was still multible is many way. In particular, it was possible to change the data in the array even if the array could not be resized. You could still call things like `WritePortal` and `PrepareForInOut`. The fact that you could change it for some things and not others was confusing. The fact that you could call `PrepareForInOut` but not `PrepareForOutput` was doubly confusing. 3. Passing a value by constant reference should be the same, from the calling code's perspective, as passing by value. Although the function can change an argument passed by value, that change is not propogated back to the calling code. However, in the case of `ArrayHandle`, calling by value would allow the array to be reallocated from the calling side whereas a constant reference would prevent that. This change makes the two behaviors consistent. 4. The supposed assurance that the `ArrayHandle` would not be reallocated was easy to break even accidentally. If the `ArrayHandle` was assigned to another `ArrayHandle` (for example as a class' member or wrapped inside of an `UnknownArrayHandle`), then the array was free to be reallocated.