chore: Update langflow template field base.py

Refactor langflow template field base.py to improve code readability and maintainability.

- Import additional types from langflow.helpers.custom and langflow.type_extraction.type_extraction modules.
- Add field_validator method to validate field_type.
- Convert type to string if it is a type instance.
- Raise ValueError if type is not a string or a type instance.

src/backend/base/langflow/template/field/base.py

@@ -1,11 +1,12 @@
 from enum import Enum
-from typing import Optional  # type: ignore
-from typing import Any, Callable, Union
+from typing import Any, Callable, GenericAlias, Optional, Union, _GenericAlias, _UnionGenericAlias  # type: ignore
 
 from pydantic import BaseModel, ConfigDict, Field, field_serializer, field_validator, model_serializer, model_validator
 
 from langflow.field_typing import Text
 from langflow.field_typing.range_spec import RangeSpec
+from langflow.helpers.custom import format_type
+from langflow.type_extraction.type_extraction import post_process_type
 
 
 class UndefinedType(Enum):
@@ -139,6 +140,19 @@ class Input(BaseModel):
             for file_type in value
         ]
 
+    @field_validator("field_type", mode="before")
+    @classmethod
+    def validate_type(cls, v):
+        # If the user passes CustomComponent as a type insteado of "CustomComponent" we need to convert it to a string
+        # this should be done for all types
+        # How to check if v is a type?
+        if isinstance(v, (type, _GenericAlias, GenericAlias, _UnionGenericAlias)):
+            v = post_process_type(v)[0]
+            v = format_type(v)
+        elif not isinstance(v, str):
+            raise ValueError(f"type must be a string or a type, not {type(v)}")
+        return v
+
 
 class Output(BaseModel):
     types: Optional[list[str]] = Field(default=[])