Adding fine-tuning models to LUKE (#18353)

* add LUKE models for downstream tasks

* add new LUKE models to docs

* fix typos

* remove commented lines

* exclude None items from tuple return values

docs/source/en/model_doc/luke.mdx

@@ -152,3 +152,23 @@ This model was contributed by [ikuyamada](https://huggingface.co/ikuyamada) and
 
 [[autodoc]] LukeForEntitySpanClassification
     - forward
+
+## LukeForSequenceClassification
+
+[[autodoc]] LukeForSequenceClassification
+    - forward
+
+## LukeForMultipleChoice
+
+[[autodoc]] LukeForMultipleChoice
+    - forward
+
+## LukeForTokenClassification
+
+[[autodoc]] LukeForTokenClassification
+    - forward
+
+## LukeForQuestionAnswering
+
+[[autodoc]] LukeForQuestionAnswering
+    - forward