Create encoders and decoders for alter table row transformer, then create
and return the row transformer.
This is code common to alter table DDL descriptors.
tableVersion - the version of the tables in the transformation.
sourceKeyOrdering - the key ordering of the source table.
targetKeyOrdering - the key ordering of the target table.
columnMapping - the one-based column mapping from source table to the
the target table, e.g.,
[1,2,4,6] indicates columns 3 and 5 were dropped and
the new table columns, which has 4 columns instead of 6,
should come from the given set of columns, in order they're
srcRow - the source exec row template.
templateRow - the target exec row template.
keyEncoder - the key encoder to use when not dealing with PKs - key is HBase rowKey.
the row transformer initialized and ready to accept rows to transform.