Many arrays decorate other arrays but still allow an efficient component
extraction. However, the component can only be extracted if it can be
efficiently extracted from the array being decorated. In this case, the
array reported that it could efficiently extract even though it could
not.
Fixed this by having the `ArrayExtractComponentImpl` classes inherit
from the respective superclass. This will in turn inhert the
`ArrayExtractComponentImplInefficient` if it is the base class.
To avoid having to use a device compiler every time you wish to use
`ArrayGetValue`, the actual implementation is compiled into the `vtkm_cont`
library. To allow this to work for all the templated versions of
`ArrayHandle`, the implementation uses the extract component features of
`UnknownArrayHandle`. This works for most common arrays, but not all
arrays.
For arrays that cannot be directly represented by an `ArrayHandleStride`,
the fallback is bad. The entire array has to be pulled to the host and then
copied serially to a basic array.
For `ArrayGetValue`, this is just silly. So, for arrays that cannot be
simply represented by `ArrayHandleStride`, make a fallback that just uses
`ReadPortal` to get the data. Often this is not the most efficient method,
but it is better than the current alternative.
The typical use case of `ArrayHandleStride` is to flexibly point into
another array, often looking at a single component in an array. It is
typical that multiple things will be accessing the same array, and bad
things could happen as they all try to resize. There was some code to
try to figure out what the size of the original array was, but it was
fragile.
It is safer for now to disable the behavior altogether. If a use case
pops up, we can reintroduce the code.
`ArrayExtractComponent` allows you to get a component of an array.
Unlike `ArrayHandleExtractComponent`, the type you get is always the
same: an `ArrayHandleStride`. This way, you can get an array that
contains the data of an extracted component with less templating and
potentially dramatically reduce the amount of code generated (although
some runtime integer arithmetic is added).
