Simplify XAdapterModel implementations (#641)

This PR includes some refactorings of all AdapterModel classes:
- moves prediction head adding methods to base mixin & remove from all
model classes
- convert `head_types` to list, use single mapping in base mixin

docs/conf.py

@@ -5,6 +5,7 @@
 # https://www.sphinx-doc.org/en/main/usage/configuration.html
 import os
 import sys
+import re
 
 
 # -- Path setup --------------------------------------------------------------
@@ -87,6 +88,21 @@
 smv_remote_whitelist = None
 
 
+def skip_head_member(app, what, name, obj, skip, options):
+    if type(obj).__name__ == "function" and "inherited-members" in options and (m := re.match(r"add\_(.*)\_head$", name)):
+        cls_name = options["inherited-members"].replace("PreTrainedModel", "AdapterModel").replace("PretrainedModel", "AdapterModel")
+        cls = vars(sys.modules["adapters"])[cls_name]
+        # HACK: currently parses head type from name
+        head_type_str = m.group(1).replace("qa", "question_answering")
+        if head_type_str in cls.head_types:
+            return False
+        else:
+            return True
+
+    return skip
+
+
 def setup(app):
+    app.connect('autodoc-skip-member', skip_head_member)
     app.add_config_value("recommonmark_config", {"enable_eval_rst": True}, True)
     app.add_css_file("custom.css")

src/adapters/heads/__init__.py

@@ -2,3 +2,4 @@
 from .base import *
 from .dependency_parsing import *
 from .language_modeling import BertStyleMaskedLMHead, CausalLMHead, Seq2SeqLMHead
+from .model_mixin import ModelWithFlexibleHeadsAdaptersMixin