Pass in a custom LoadingManager for progress reporting.
Load glTF from a URL. Only the main file is loaded - external buffer and image files
are loaded lazily when needed. To load all, you can use GltfAsset.preFetchAll()
Load from Files you might get from a file input or via drag-and-drop.
fileMap is expected to map from a full file path (including directories if present).
This matches the format provided by simple-dropzone.
If you don't need support for directories/zip files, you can use File.name as the key.
Note that preFetchAll is called on the result GltfAsset before returning it so that
the uploaded files can be garbage-collected immediately.
Main class of the library