[brightball]

There is some editor plugin that converts it visually to a triangle. I have seen other people use it.

[arrowsmith]

It’s a font, not an editor plugin.

Not sure which font specifically is used in the article but an example of a monospace font with ligatures is Fira: https://github.com/tonsky/FiraCode

[lvass]

prettify-symbols-mode in Emacs.