AssetLoader should be extendable by chaining multiple format loaders

## What problem does this solve or what need does it fill?

Related to #21185 and #24130

GltfLoader and CompressedImageSaver processor uses ImageLoader, which doesn't support custom image asset loader, and hdr, exr loaders.

In this case, we want a centralized image loader that contains multiple format loaders, chaining them to check file extensions or read bytes to determine if an Image can be loaded.

## What solution would you like?

This is a very rough idea:

1. AssetFormatLoader for recognizing and loading one format.
2. AssetLoader which chains multiple AssetFormatLoader and can be extended by users. If a format loader fails we try the next instead of failing to load.

Review the existing GltfLoader, CompressedImageSaver, and ImageLoader implementations, then read related issues #21185 and #24130 for context. Define how centralized image loading should recognize formats, try multiple loaders, and allow custom loaders, including hdr and exr support; done means the proposed loader covers these cases without failing after the first unsupported format.

Written by the indexing model from the issue text.