Split LICENSE addendum by derivation type (#20222)
## Summary
Per
https://github.com/astral-sh/ruff/issues/20191#issuecomment-3251131478,
this PR restructures the license file to draw a distinction between
projects from which we've (e.g.) drawn source code and projects whose
rules we've implemented but have otherwise not reused or adapted source
code from, which are credited in the README. While I was here, I also
sorted the list.
