Removed obsolete warning about mixins in the doc

Remove dead module Distribution.Client.Compat.FilePerms

Fix missing space in error message

Add the missing space in error messages like:
```
  (conflict: requires NumDecimalswhich is not supported)
```

Reduce VCS QuickCheck count to 10 (from 100)

CI times appear to be dominated by the CI tests, which seems
excessive.

A typical Linux validate.sh job takes ~45 minutes, of which
15 are spent in the VCS tests. MacOS is even worse, with the
VCS tests taking >1h out of a total time of >2h.

Simplify bootstrap generation

- Remove the .plan.json files, since they're just intermediate files.
- Remove the Linux check since e.g. macOS works just fine.

addFileMode: Replace use of Posix.Internals module with public API

Split --repl-options on whitespace

Function `words` used instead of cons operator which was just adding
full string value to an empty array.

Improve names of generated executables for scripts

Fix haddock via Setup.hs with internal libraries

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

docs: cabal.project in parent directories

Co-authored-by: Andreas Abel <andreas.abel@ifi.lmu.de>