Since recently it's possible to access assets from outside the File/Asset Browser, via the asset view template. So we are slowly moving away from file space specific code to dedicated asset system code. I introduced `AssetLibraryReference` as a duplicate of `FileSelectAssetLibraryUID`, with a plan to delete the latter in a separate cleanup commit. That's exactly what this commit is. This will cause Asset Browsers to open with the default "Current File" Asset Library. We could avoid that, but it's a minor issue really.