Precompiled field map permutation and averaging

Provided a pair of functions, MapFieldPermutation and MapFieldMergeAverage that do the most common operations for the MapFieldOntoOutput stage of filter execution (other than doing nothing). These methods are precompiled into the vtkm_filter library. Although they only use the default policy (they do not respect custom policies), they are pre-compiled with all possible types basic types (up to a Vec size of 4).

Even though the new versions support more field types, the compile time is about the same as before.