This adds a name-based field mode to the Row class. A row can
operate in 3 different modes: name-based, position-based, or
a hybrid of both when leaving the Flink runtime. It simplifies
the handling of large rows (possibly with hundreds of fields)
and will make it easier to switch between DataStream API and
Table API.

See the documentation of the Row class for more information.

This closes #14420.