Modernize build script for compatibility with current tools

[retowyss]

Changes

This PR updates the build script to be compatible with current versions of fontmake, gftools, and other font building tools.

Improvements:

• Removed deprecated gftools commands
• Added conditional checks to only run commands if they're available
• Improved path handling
• Enhanced progress reporting
• Used arrays and helper functions
• Added safety checks

Testing

• Tested in Docker environment with current tool versions (gftools 0.9.81+)
• Confirmed that font naming conventions are preserved (including the Heavy/Hevy naming)

Misc

I also created a docker based build script for our purposes, I can submit it if you are interested.
Thanks,

Reto