Geometry issues in BoomBoxWithAxes

- Plus signs have holes in the corners.
- Letters have strange irregularities on the flat surfaces.
- The scene size is too small considering the glTF units convention.


/cc @bghgary

Start by locating the BoomBoxWithAxes asset in the repository and reviewing the attached image. Investigate the asset geometry for the corner holes and irregular flat surfaces, then check its scene scale against the glTF units convention. Done means all three reported geometry and scale issues are corrected and the resulting asset can be visually verified.

Written by the indexing model from the issue text.