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/aphrodite.py

@@ -3,7 +3,8 @@ from typing import Any, Dict, List, Optional
 from langchain_core.callbacks import CallbackManagerForLLMRun
 from langchain_core.language_models import BaseLLM
 from langchain_core.outputs import Generation, LLMResult
-from langchain_core.pydantic_v1 import Field, root_validator
+from langchain_core.pydantic_v1 import Field
+from langchain_core.utils import pre_init
 
 
 class Aphrodite(BaseLLM):
@@ -157,7 +158,7 @@ class Aphrodite(BaseLLM):
 
     client: Any  #: :meta private:
 
-    @root_validator()
+    @pre_init
     def validate_environment(cls, values: Dict) -> Dict:
         """Validate that python package exists in environment."""