Improve handling of a symlinked application directory#557

Draft

intelfx wants to merge 3 commits intoflatpak:mainfrom

intelfx:work/better-app-dir

Commits on Jul 23, 2023

Do not remove the target directory on --force-clean; only clear it
intelfx
committed
Fix same-filesystem check on the state and app directories
intelfx
committed
Do not remove the target directory in builder_cache_checkout(); only clear it
intelfx
committed