AmrArrays filter should store fields as ArrayHandleConstant

MR !3114 (merged) allows filters to extract a component of an ArrayHandleConstant without knowing it is that array type and without copying the data. With that functionality in place, it is reasonable for filters like AmrArrays to store constant arrays natively in fields.

AmrArrays stores multiple cell field arrays that have constant values. It currently does this by filling a basic array with a constant value. However, it would save much memory to just store the arrays as an ArrayHandleConstant and allow downstream filters to handle the data.

Note that there might be some filters that assume the data are in a basic array. These might have to be modified to ensure the handle the field correctly.