Filament does not yet fully support threads with WASM, but this is a
baby step in that direction.
To enable experimental pthreads support, enable the WEBGL_PTHREADS CMake
option. This will enable pthreads support in `gltfio` and `utils`, which
is known to work, but not when served with GitHub Pages.
The web server must emit COOP, COEP and CORP headers, so our build
instructions now recommend the use of `emrun` for local testing.
This also changes our demos so that they do not use unpkg, which
does not work when using `emrun`, due to cross-origin restrictions.
After the native async functionality landed, there was no way for web
clients to be notified that the decoding has finished. This PR changes
the existing `onDone` callback so that it gets called after all textures
have been decoded. (Previously it was called after downloading rather
than decoding.)
This has the side effect of simplifying the API because clients no
longer need to call a finalize function.
