exec: support nodenv, pyenv and rbenv

[carlocab]

If nodenv, pyenv, or rbenv are in the Brewfile, let's add their
shims directory to PATH during brew bundle exec.

This makes it so that brew bundle exec just works without relying on
the user adding the required node/python3/ruby formula to their
Brewfile and then doing brew *env-sync.

[jacobbednarz]

i like the intention here however, it seems like we may be playing a game of whack a mole with all version managers that rely on shims. should we expand the coverage for more tools upfront?

[carlocab]

I'd rather not. These are the version managers that are well-integrated with brew given that they have supporting built-in commands:

• https://github.com/Homebrew/brew/blob/9978c3d11ac9108940ee0976a362d0d5872e0916/Library/Homebrew/cmd/nodenv-sync.rb
• https://github.com/Homebrew/brew/blob/9978c3d11ac9108940ee0976a362d0d5872e0916/Library/Homebrew/cmd/pyenv-sync.rb
• https://github.com/Homebrew/brew/blob/9978c3d11ac9108940ee0976a362d0d5872e0916/Library/Homebrew/cmd/rbenv-sync.rb

Other version managers not only aren't integrated as well with brew, and some also don't support usage through brew.

To avoid the whack-a-mole, we can probably draw the line at anything that already has native brew integration.

[jacobbednarz]

sounds great, thanks @carlocab

[MikeMcQuaid]

@carlocab Thanks! Let's not go much further in this direction, though; don't want Brewfile scope to expand too much.