Integrate featurizers (#1573)
Added Sample Featurizer and Infrastructure
Make featurizers and unit tests compile and run with GTest.
Create definitions for the first featurizer kernel.
Add new operator domain.
Create datetime_transformer kernel and build.
Move OPAQUE types definitions for featurizers kerneles out to a separate cc.
Register them with the type system.
Provide unit tests for new AutoML DateTimeTransformer kernel.
Make necessary adjustments to the test infrastructure to make it run
with new types.
