Clean up multi repo build hacks with Lerna

[BurtHarris]

The Lerna package is designed to address challenges in multi-package repos, like this one. It seems to have matured significantly since the last time I looked at it.

I believe it would be a much cleaner solution to the antlr4ts-cli dependency in building the antlr4ts run time than the current hack of using npm link/unlink commands.

[BurtHarris]

I've been working with Lerna now for months. Some good experience, some not so good. I just found out that the alternative package manager pnpm may be a good alternative