Adding generics to the Java API - Phase 1 (#11251)

* Phase 1 of the proposed generic Java API.

This adds new classes to represent each of the possible tensor types,
and some scripting support for generating those classes. There is
essentially no effect on existing classes, except that DataType is
made slightly more efficient.

All tests pass.

* Addressed Asim's review.

* Hoisted copyright into a separate declaration. Maybe it should go
in a separate file?

* Added private constructors to TF types and shortened their javadoc to be
more standard.

* Added more explanation about the enum relationship.

* Used more-idiomatic import statement.

* Rename zero column.

* Removed the datatype code from tftypes.csv

* Fix the default value for Double, add one for UInt8.

* Got rid of 'boxed type' column in CSV file

* Somehow I did not notice that TFType.java was not checked in.