The other modifications are useless, they simply make hel-arabic
dependent on arabic.ly. But hel-arabic.ly is supposed to be an
independent file from other ly files.
This doesn't make sense. `hel-arabic.ly` is part of the LilyPond core
files. If someone uses a recent version of LilyPond, both
`hel-arabic.ly` and `arabic.ly` are *always* present. *Of course* it
should share the code with `arabic.ly`! Our goal is to improve
maintainability, and avoiding duplicated code is definitely such an
improvement.
Werner