Adding the state-of-the-art contrastive search decoding methods for the codebase of generation_utils.py (#19477)

* add: the contrastive search for generaton_utils

* add: testing scripts for contrastive search under examples/text-generation

* update the quality of codes

* revise the docstring; make the generation_contrastive_search.py scripts;

* revise the examples/pytorch/text-generation/run_generation_contrastive_search.py to the auto-APIs format

* revise the necessary documents

* fix: revise the docstring of generation_contrastive_search.py

* Fix the code indentation

* fix: revise the nits and examples in contrastive_search docstring.

* fix the copyright

* delete generation_contrastive_search.py

* revise the logic in contrastive_search

* update the intergration test and the docstring

* run the tests over

* add the slow decorate to the contrastive_search intergrate test

* add more test

* do the style, quality, consistency checks

docs/source/en/internal/generation_utils.mdx

@@ -14,6 +14,7 @@ specific language governing permissions and limitations under the License.
 
 This page lists all the utility functions used by [`~generation_utils.GenerationMixin.generate`],
 [`~generation_utils.GenerationMixin.greedy_search`],
+[`~generation_utils.GenerationMixin.contrastive_search`],
 [`~generation_utils.GenerationMixin.sample`],
 [`~generation_utils.GenerationMixin.beam_search`],
 [`~generation_utils.GenerationMixin.beam_sample`],

docs/source/en/main_classes/text_generation.mdx

@@ -26,6 +26,7 @@ Each framework has a generate method for auto-regressive text generation impleme
 	- sample
 	- beam_search
 	- beam_sample
+	- contrastive_search
 	- group_beam_search
 	- constrained_beam_search