Opt in flax and tf (#17388)

* initial commit

* add init file

* update globakl init

* update index and dummy objects

* style

* update modelling auto

* fix initi typo in src/transformers

* fix typo in modeling tf auto, opt was in wrong mapping name

* fixed a slow test : saved_model

* style

* fix positionnal embedding if no position id is provided

* update tf test

* update test flax requirements

* fixed serialization

* update

* update tf name to allow smooth convertion

* update flax tests

* style

* fix test typo

* fix tf typo test

* add xla for generate support in causal LM

* fixed bug

* cleaned tf tests

* style

* removed from PT for slow tests

* fix typp

* opt test as slow

* trying to fix GPT2 undefined

* correct documentation and add to test doc

* update tf doc

* fix doc

* fake commit

* Apply suggestions from code review

Co-authored-by: Joao Gante <joaofranciscocardosogante@gmail.com>

* update test based on review

* merged main layer for functionning test

* fixup + quality

* Apply suggestions from code review

Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>

* update long comment

* make fix copies

Co-authored-by: Arthur <arthur@huggingface.co>
Co-authored-by: Joao Gante <joaofranciscocardosogante@gmail.com>
Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>

tests/models/opt/test_modeling_opt.py

@@ -334,7 +334,7 @@ class OPTGenerationTest(unittest.TestCase):
     @property
     def prompts(self):
         return [
-            "Today is a beautiful day and I want to",
+            "Today is a beautiful day and I want",
             "In the city of",
             "Paris is the capital of France and",
             "Computers and mobile phones have taken",
@@ -344,7 +344,7 @@ class OPTGenerationTest(unittest.TestCase):
         model_id = "facebook/opt-125m"
 
         EXPECTED_OUTPUTS = [
-            "Today is a beautiful day and I want to thank",
+            "Today is a beautiful day and I want everyone",
             "In the city of Rome Canaver Canaver Canaver Canaver",
             "Paris is the capital of France and Parisdylib",
             "Computers and mobile phones have taken precedence over",
@@ -409,7 +409,7 @@ class OPTGenerationTest(unittest.TestCase):
         model_id = "facebook/opt-350m"
 
         EXPECTED_OUTPUTS = [
-            "Today is a beautiful day and I want to share",
+            "Today is a beautiful day and I want to",
             "In the city of San Francisco, the city",
             "Paris is the capital of France and the capital",
             "Computers and mobile phones have taken over the",