feat(api): Add image multimodal support for LLMNode (#17372)

Enhance `LLMNode` with multimodal capability, introducing support for
image outputs.

This implementation extracts base64-encoded images from LLM responses,
saves them to the storage service, and records the file metadata in the
`ToolFile` table. In conversations, these images are rendered as
markdown-based inline images.
Additionally, the images are included in the LLMNode's output as
file variables, enabling subsequent nodes in the workflow to utilize them.

To integrate file outputs into workflows, adjustments to the frontend code
are necessary.

For multimodal output functionality, updates to related model configurations
are required. Currently, this capability has been applied exclusively to
Google's Gemini models.

Close #15814.

Signed-off-by: -LAN- <laipz8200@outlook.com>
Co-authored-by: -LAN- <laipz8200@outlook.com>

api/core/file/file_manager.py

@@ -10,12 +10,12 @@ from core.model_runtime.entities import (
     VideoPromptMessageContent,
 )
 from core.model_runtime.entities.message_entities import PromptMessageContentUnionTypes
+from core.tools.signature import sign_tool_file
 from extensions.ext_storage import storage
 
 from . import helpers
 from .enums import FileAttribute
 from .models import File, FileTransferMethod, FileType
-from .tool_file_parser import ToolFileParser
 
 
 def get_attr(*, file: File, attr: FileAttribute):
@@ -130,6 +130,6 @@ def _to_url(f: File, /):
         # add sign url
         if f.related_id is None or f.extension is None:
             raise ValueError("Missing file related_id or extension")
-        return ToolFileParser.get_tool_file_manager().sign_file(tool_file_id=f.related_id, extension=f.extension)
+        return sign_tool_file(tool_file_id=f.related_id, extension=f.extension)
     else:
         raise ValueError(f"Unsupported transfer method: {f.transfer_method}")