community[patch]: Use get_fields adapter for pydantic (#25191)

Change all usages of __fields__ with get_fields adapter merged into
langchain_core.

Code mod generated using the following grit pattern:

```
engine marzano(0.1)
language python


`$X.__fields__` => `get_fields($X)` where {
    add_import(source="langchain_core.utils.pydantic", name="get_fields")
}
```

libs/community/langchain_community/llms/modal.py

@@ -5,6 +5,7 @@ import requests
 from langchain_core.callbacks import CallbackManagerForLLMRun
 from langchain_core.language_models.llms import LLM
 from langchain_core.pydantic_v1 import Field, root_validator
+from langchain_core.utils.pydantic import get_fields
 
 from langchain_community.llms.utils import enforce_stop_tokens
 
@@ -40,7 +41,7 @@ class Modal(LLM):
     @root_validator(pre=True)
     def build_extra(cls, values: Dict[str, Any]) -> Dict[str, Any]:
         """Build extra kwargs from additional params that were passed in."""
-        all_required_field_names = {field.alias for field in cls.__fields__.values()}
+        all_required_field_names = {field.alias for field in get_fields(cls).values()}
 
         extra = values.get("model_kwargs", {})
         for field_name in list(values):