Replace the load_folder API by load_batch

[shishanyue]

Objective

About #19727

Solution

• Remove load_folder API,LoadedFolder and so on
• add LoadedBatch ,LoadBatchRequest
• use the crate glob

Testing

-rewrite the example texture_atlas.rs

//before
// Load multiple, individual sprites from a folder
commands.insert_resource(RpgSpriteFolder(asset_server.load_folder("textures/rpg")));

//now
commands.insert_resource(RpgSpriteFolder(asset_server.load_batch(
    LoadBatchRequest::new(vec!["textures/rpg/**/*", "textures/rpg/chars/**/*"]),
)));

Problem

But there have a problem.I can't get the base path.I need in load_batch_internal to glob the all file.

format!("assets/{}", request_path)

How can I obtain the unprocessed_path and processed_path under load_batch? I have used the crate glob. If I want to use it, I must prepend 'assets' to the path. However, it is evident that we can change it, and even add additional paths like in extra_file. Therefore, I need to retrieve the corresponding full path through AssetPath in load_batch. But I cannot find any method to achieve this.