add support for toggling line numbers on and off

[ben-p-commits]

Description

Adds support for #115, ✨Option To Hide Line Numbers. Simply shows/hides ruler view. should be easy enough in the future to include affordances for enabling/disabling code folding ribbon, code review, other rulerview utilities once they come into play.

Demo

[austincondiff]

Should we also shift all content to the left when the line numbers are hidden? Is the space the line numbers were consuming not necessary anymore?

It looks like Xcode does this...

https://user-images.githubusercontent.com/806104/214165962-b9442b9c-0b43-4d04-8cec-1d524e488f50.mov

[ben-p-commits]

@austincondiff - ooh okay, i'll see what I can do

[ben-p-commits]

Update: created a PR over in STTextView to enable this behavior without introducing code smell in CETV...

https://github.com/krzyzanowskim/STTextView/pull/11

@austincondiff - if we can get that change approved: we get the improved behavior:

https://user-images.githubusercontent.com/5067237/214394396-d727682a-f35e-44c9-9204-da3369d67234.mp4

[lukepistrol]

@ben-p-commits Ok lets wait for the outcome of the PR on STTextView for now.

[ben-p-commits]

@lukepistrol, closing this in light of #127