core[minor],community[minor]: Upgrade all @root_validator() to @pre_init (#23841)

This PR introduces a @pre_init decorator that's a @root_validator(pre=True) but with all the defaults populated!

libs/community/langchain_community/llms/huggingface_endpoint.py

@@ -10,7 +10,11 @@ from langchain_core.callbacks import (
 from langchain_core.language_models.llms import LLM
 from langchain_core.outputs import GenerationChunk
 from langchain_core.pydantic_v1 import Extra, Field, root_validator
-from langchain_core.utils import get_from_dict_or_env, get_pydantic_field_names
+from langchain_core.utils import (
+    get_from_dict_or_env,
+    get_pydantic_field_names,
+    pre_init,
+)
 
 logger = logging.getLogger(__name__)
 
@@ -162,7 +166,7 @@ class HuggingFaceEndpoint(LLM):
         values["model"] = values.get("endpoint_url") or values.get("repo_id")
         return values
 
-    @root_validator()
+    @pre_init
     def validate_environment(cls, values: Dict) -> Dict:
         """Validate that package is installed and that the API token is valid."""
         try: