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/embeddings/laser.py

@@ -2,7 +2,8 @@ from typing import Any, Dict, List, Optional
 
 import numpy as np
 from langchain_core.embeddings import Embeddings
-from langchain_core.pydantic_v1 import BaseModel, Extra, root_validator
+from langchain_core.pydantic_v1 import BaseModel, Extra
+from langchain_core.utils import pre_init
 
 LASER_MULTILINGUAL_MODEL: str = "laser2"
 
@@ -41,7 +42,7 @@ class LaserEmbeddings(BaseModel, Embeddings):
 
         extra = Extra.forbid
 
-    @root_validator()
+    @pre_init
     def validate_environment(cls, values: Dict) -> Dict:
         """Validate that laser_encoders has been installed."""
         try: