Ruby layer refactor and new shadowenv layer

[syl20bnr]

Related issue: https://github.com/syl20bnr/spacemacs/issues/14653

• new macro spacemacs|eval-for-enabled-ruby-mode
• use "dispatch" pattern with local vars hook for backend, test-runner, version-manager
• use spacebind
• diminish minor modes lighter
• new layer: shadowenv
• add shadowenv layer to ruby mode, python mode and compilation buffer

[syl20bnr]

I updated the conventions for toggles lighters in the mode line, see commit message https://github.com/syl20bnr/spacemacs/commit/c8ae548c9 These conventions were missing from the convention doc, this commit adds them.

[lebensterben]

Also it'd be nice if you can change (add-hook 'foo 'bar) to (add-hook 'foo #'bar) where bar is a symbol of function.

This is not strictly enforced now but is easier for byte compiler to understand such symbol is a function.

[syl20bnr]

Do not merge this yet, I'm stil working on it.

[smile13241324]

Given that this is now older than 3 years I would like to go ahead and close it for now.