LED (#9278)

* create model

* add integration

* save current state

* make integration tests pass

* add one more test

* add explanation to tests

* remove from bart

* add padding

* remove unnecessary test

* make all tests pass

* re-add cookie cutter tests

* finish PyTorch

* fix attention test

* Update tests/test_modeling_common.py

* revert change

* remove unused file

* add string to doc

* save intermediate

* make tf integration tests pass

* finish tf

* fix doc

* fix docs again

* add led to doctree

* add to auto tokenizer

* added tips for led

* make style

* apply jplus statements

* correct tf longformer

* apply lysandres suggestions

* apply sylvains suggestions

* Apply suggestions from code review

utils/check_repo.py

@@ -30,6 +30,8 @@ PATH_TO_DOC = "docs/source"
 # Being in this list is an exception and should **not** be the rule.
 IGNORE_NON_TESTED = [
     # models to ignore for not tested
+    "LEDEncoder",  # Building part of bigger (tested) model.
+    "LEDDecoder",  # Building part of bigger (tested) model.
     "BartDecoder",  # Building part of bigger (tested) model.
     "BartEncoder",  # Building part of bigger (tested) model.
     "BertLMHeadModel",  # Needs to be setup as decoder.
@@ -64,6 +66,8 @@ TEST_FILES_WITH_NO_COMMON_TESTS = [
 # should **not** be the rule.
 IGNORE_NON_AUTO_CONFIGURED = [
     # models to ignore for model xxx mapping
+    "LEDEncoder",
+    "LEDDecoder",
     "BartDecoder",
     "BartEncoder",
     "DPRContextEncoder",