Blender Addon in file menu

Question

I have created a blender addon watching videos as I do not have knowledge of python. So I want to place that addon in Blender file menu but it is deleting all the other option in that menu. Also I want to assign shortcut to that menu but I am not able to assign shortcut to it .

This is what I found in log :

bpy.data.window_managers["WinMan"].(null) = 'THREE'

Here is my code :

bl_info = {
    "name": "UV_Exporter v3.0",
    "author": "Your Name Here",
    "version": (1, 0),
    "blender": (2, 80, 0),
    "location": "File > Import-Export",
    "description": "Extract UV from Multiple Obj",
    "warning": "",
    "doc_url": "",
    "category": "Import-Export",
}


import bpy
import os

def main(context):

    # You should change this varibale in "here" to match your own directory path
    # use '/' or '\\' for hirecacy
    target_dir = "C:/Users/Arpit/Desktop/UV/" 
    selObj = []

    for obj in bpy.context.selected_objects:
        selObj.append(obj.name)
        
        
    bpy.ops.object.select_all(action='TOGGLE')
        
    for item in selObj:

        obj = bpy.context.window.scene.objects[item]
        bpy.context.view_layer.objects.active = obj
        bpy.ops.object.mode_set(mode="EDIT")
        bpy.ops.mesh.select_all(action='TOGGLE')
        bpy.ops.mesh.select_all(action='TOGGLE')

        # `item` instead of `selObj[i]`
        full_file_name = target_dir + bpy.data.objects[ item ].name
        dirname = os.path.dirname(full_file_name)

        # inside `while`-loop
        if not os.path.exists(dirname):
            os.makedirs(dirname)

        bpy.ops.uv.export_layout(filepath=full_file_name, mode='PNG', size=(1024, 1024), opacity=0.6)
        bpy.ops.object.mode_set(mode="OBJECT")
        

class UvExporter(bpy.types.Operator):
    """Tooltip"""
    bl_idname = "object.uv_exporter"
    bl_label = "UV EXPORTER"


    def execute(self, context):
        main(context)
        return {'FINISHED'}

def menu_func(self, context):
    self.layout.operator(UvExporter.bl_idname, text=UvExporter.bl_label)





class LayoutDemoPanel(bpy.types.Menu):
    """Creates a Panel in the scene context of the properties editor"""
    bl_idname = "TOPBAR_MT_file_import"
    bl_label = "Import"


    def draw(self, context):
        layout = self.layout

        scene = context.scene


        # Big render button
        row = layout.row()
        row.scale_y = 1.0
        row.operator("object.uv_exporter")



def register():
    bpy.utils.register_class(LayoutDemoPanel)
    bpy.utils.register_class(UvExporter)
    bpy.types.VIEW3D_MT_object.append(menu_func)



def unregister():
    bpy.utils.unregister_class(LayoutDemoPanel)
    bpy.utils.unregister_class(UvExporter)
    bpy.types.VIEW3D_MT_object.remove(menu_func)


if __name__ == "__main__":
    register()

Please help me with this.