Add XGLM models (#14876)

* add xglm

* update vocab size

* fix model name

* style and tokenizer

* typo

* no mask token

* fix pos embed compute

* fix args

* fix tokenizer

* fix positions

* fix tokenization

* style and dic fixes

* fix imports

* add fast tokenizer

* update names

* add pt tests

* fix tokenizer

* fix typo

* fix tokenizer import

* fix fast tokenizer

* fix tokenizer

* fix converter

* add tokenizer test

* update checkpoint names

* fix tokenizer tests

* fix slow tests

* add copied from comments

* rst -> mdx

* flax model

* update flax tests

* quality

* style

* doc

* update index and readme

* fix copies

* fix doc

* update toctrr

* fix indent

* minor fixes

* fix config doc

* don't save embed_pos weights

* Apply suggestions from code review

Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>
Co-authored-by: Patrick von Platen <patrick.v.platen@gmail.com>

* address Sylvains commnets, few doc fixes

* fix check_repo

* align order of arguments

* fix copies

* fix labels

* remove unnecessary mapping

* fix saving tokenizer

Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>
Co-authored-by: Patrick von Platen <patrick.v.platen@gmail.com>

docs/source/_toctree.yml

@@ -304,6 +304,8 @@
       title: Wav2Vec2Phoneme
     - local: model_doc/wavlm
       title: WavLM
+    - local: model_doc/xglm
+      title: XGLM
     - local: model_doc/xlm
       title: XLM
     - local: model_doc/xlm-prophetnet