[tf.data] Move the C++ Dataset class implementations to the framework library.

This enables the use of the `DatasetOpKernel` subclasses in custom op library
code. A subsequent change will move `tf.contrib.data` kernel implementations
to a custom op library.

Implementation note: This change moves some classes from
"tensorflow/core/graph/..." into the framework library, which does not
include any code in "tensorflow/core/common_runtime/...". To break the
dependency from "tensorflow/core/framework/dataset.cc" to
"tensorflow/core/common_runtime/...", the `GraphDefBuilderToGraph()`
method has been split out from the `GraphDefBuilder` class (where it
was previously exposed as the `GraphDefBuilder::ToGraph()` utility
method) and added to a new
"tensorflow/core/graph/graph_def_builder_util.h" module.  This method
depends on ".../graph/graph_constructor.cc", which depends directly on
".../common_runtime/shape_refiner.h" and indirectly on
".../common_runtime/graph_runner.h". Since this method was used only
in tests, these have been updated to point to the new utility method.

PiperOrigin-RevId: 184888903