The `demo_*` web samples were using unpkg to refer to the Filament build
rather than using the local copy, which was inconsistent with the other
web samples.
We now use the local copy of Filament for everything except the
drag-and-drop viewer, which always uses the latest version of Filament.
This makes the tutorials more consistent with the live demos and lets us
more easily ensure that the tutorials are kept up to date without
errors. In fact it caught an error in the Suzanne tutorial.
Since this affects source rather than served files, this PR is intended
for main. The master branch will be updated in a subsequent PR.
