Fix #3024: repl alias in sbt and dist/bin/dotr not working

[felixmulder]

We should also decide if we should ditch the old ./bin scripts in favor of the ./dist/bin scripts. Keeping both up to date feels tedious.

[liufengyun]

LGTM

Regarding bin/dotc and bin/dotr, if nobody is using them, we can remove.

[rom1dep]

I just discovered about ./dist/bin, it doesn't do anything here but printing errors about missing dotty/dist/lib/’.

If I had a vote for saving either, it would go to ./bin :)

[liufengyun]

@rom1dep dist/bin is mainly for releasing Dotty packages. To try it, you need to first run sbt dist/pack then run dist/target/pack/bin/dotr.

For development, we usually run dotc from sbt, thus no script is needed for development.

[rom1dep]

OK, I've been having ./bin in my path for a while and was appreciating the convenience of it triggering a rebuild as required. As my sole contribution here consists of fiddling with dotty's repl a few times a week/month, that's indeed not a strong defense for the extra maintenance cost :)