Adds LlamaForQuestionAnswering class in modeling_llama.py along with AutoModel Support (#28777)

* This is a test commit

* testing commit

* final commit with some changes

* Removed copy statement

* Fixed formatting issues

* Fixed error added past_key_values in the forward method

* Fixed a trailing whitespace. Damn the formatting rules are strict

* Added the copy statement

tests/models/llama/test_modeling_llama.py

@@ -44,6 +44,7 @@ if is_torch_available():
     from transformers import (
         CodeLlamaTokenizer,
         LlamaForCausalLM,
+        LlamaForQuestionAnswering,
         LlamaForSequenceClassification,
         LlamaModel,
         LlamaTokenizer,
@@ -278,7 +279,11 @@ class LlamaModelTester:
 
 @require_torch
 class LlamaModelTest(ModelTesterMixin, GenerationTesterMixin, PipelineTesterMixin, unittest.TestCase):
-    all_model_classes = (LlamaModel, LlamaForCausalLM, LlamaForSequenceClassification) if is_torch_available() else ()
+    all_model_classes = (
+        (LlamaModel, LlamaForCausalLM, LlamaForSequenceClassification, LlamaForQuestionAnswering)
+        if is_torch_available()
+        else ()
+    )
     all_generative_model_classes = (LlamaForCausalLM,) if is_torch_available() else ()
     pipeline_model_mapping = (
         {
@@ -286,6 +291,7 @@ class LlamaModelTest(ModelTesterMixin, GenerationTesterMixin, PipelineTesterMixi
             "text-classification": LlamaForSequenceClassification,
             "text-generation": LlamaForCausalLM,
             "zero-shot": LlamaForSequenceClassification,
+            "question-answering": LlamaForQuestionAnswering,
         }
         if is_torch_available()
         else {}