IO: Use FileHandler in Node Editors

Use `FileHandlers` to handle file drag-n-drop in Node Editors. Drop-boxes
still remain since they handle Images ID drag-n-drop.

This also allows to open/drag-n-drop multiple files at once.

Also this will allow add-ons to also support drag-n-drop for images and
movies in node editors while still providing access to Blender's native
support since File Handlers let users choose which to invoke if there's
multiple configured.

Pull Request: https://projects.blender.org/blender/blender/pulls/121051

scripts/startup/bl_operators/node.py

@@ -6,6 +6,7 @@ from __future__ import annotations
 
 import bpy
 from bpy.types import (
+    FileHandler,
     Operator,
     PropertyGroup,
 )
@@ -441,9 +442,27 @@ class NODE_OT_enum_definition_item_move(Operator):
         return {'FINISHED'}
 
 
+class NODE_FH_image_node(FileHandler):
+    bl_idname = "NODE_FH_image_node"
+    bl_label = "Image node"
+    bl_import_operator = "node.add_file"
+    bl_file_extensions = ";".join((*bpy.path.extensions_image, *bpy.path.extensions_movie))
+
+    @classmethod
+    def poll_drop(cls, context):
+        return (
+            (context.area is not None) and
+            (context.area.type == 'NODE_EDITOR') and
+            (context.region is not None) and
+            (context.region.type == 'WINDOW')
+        )
+
+
 classes = (
     NodeSetting,
 
+    NODE_FH_image_node,
+
     NODE_OT_add_node,
     NODE_OT_add_simulation_zone,
     NODE_OT_add_repeat_zone,