Change CellAverage and PointAverage to work on fields of any type

The previous versions of these filters used a float fallback to handle most array types. The problem with this approach other than converting field types perhaps unexpectantly is that it does not work with every Vec size. This change uses the extract by component feature of UnknownArrayHandle to handle every array type.

To implement this change the CellAverage worklet had to be changed to handle recombined vecs. This change resulted in a feature degridation where it can no longer be compiled for inputs of incompatible Vec sizes. This feature dates back to when worklets like this were exposed in the interface. This worklet class is now hidden away from the exposed interface, so this degredation should not affect end users. There are some unit tests that use this worklet to test other features, and these had to be updated.