Support both SV2 and SV4 in VectorizedCopyOperator

[bobluppes]

At this moment, the implementation of the VectorizedCopyOperator is altered to work with 4 byte selection vectors instead of 2 byte vectors.

Based on the selection vector mode of the incoming schema, the copy operator could select to either use the SV2 or SV4 implementation with corresponding implementations for the FieldBufferCopiers.